Effects of H2O2 on the growth, secretion, and metabolism of hybridoma cells in culture

Extracellular H2O2, peroxiredoxin, and glutathione reductase alter Neospora caninum invasion and proliferation in Vero cells

Neospora caninum is a protozoan member of the Apicomplexa phylum and is closely connected with abortion in cattle. The development of the parasite in host cells is characterized by the active secretion of proteins, allied to the tight control of the redox status. In this sense, elucidating the mechanisms related to the role of the redox agents and enzymes during the invasion and proliferation of N. caninum may contribute to developing novel forms of neosporosis control. In this study we verified the effects of the recombinant forms of N. caninum glutathione reductase (rNcGR) and thioredoxin-dependent peroxide reductase (rNcPrx), as well as H₂O₂ in the tachyzoite invasion and proliferation. rNcPrx interfered in the N. caninum invasion in a redox state manner. Oxidized rNcPrx inhibited the N. caninum invasion and proliferation with no toxic effects observed in Vero cells. In contrast, lower concentrations of H₂O₂ (10 μM) stimulated the N. caninum invasion, which was reverted in higher doses (>100 μM). H₂O₂ inhibited the parasite proliferation in lower concentrations than cytotoxicity in host cells, resulting in a positive selectivity index (1.8). Besides, rNcPrx (reduced and non-reduced) and rNcGR inhibited the parasite proliferation without affecting the host cell. Our results indicate the connection between the N. caninum development and the redox state, contributing to the elucidation of parasite propagation and control mechanisms.

Regulatory roles of glutathione-S-transferases and 4-hydroxynonenal in stress-mediated signaling and toxicity

Glutathione-S-Transferases (GSTs) have primarily been thought to be xenobiotic metabolizing enzymes that protect cells from toxic drugs and environmental electrophiles. However, in last three decades, these enzymes have emerged as the regulators of oxidative stress-induced signaling and toxicity. 4-Hydroxy-trans 2-nonenal (HNE) an end-product of lipid peroxidation, has been shown to be a major determinant of oxidative stress-induced signaling and toxicity. HNE is involved in signaling pathways, including apoptosis, proliferation, modulation of gene expression, activation of transcription factors/repressors, cell cycle arrest, and differentiation. In this article, available evidence for a major role of GSTs in the regulation of HNE-mediated cell signaling processes through modulation of the intracellular levels of HNE is discussed.

Vulnerability of central neurons to secondary insults after in vitro mechanical stretch

Mild traumatic brain injuries are of major public health significance. Neurons in such injuries often survive the primary mechanical deformation only to succumb to subsequent insults. To study mechanisms of vulnerability of injured neurons to secondary insults, we used an in vitro model of sublethal mechanical stretch. Stretch enhanced the vulnerability of the neurons to excitotoxic insults, causing nuclear irregularities, DNA fragmentation, and death suggestive of apoptosis. However, the DNA degradation was not attributable to classical (caspase mediated) or caspase-independent apoptosis. Rather, it was associated with profound stretch-induced mitochondrial dysfunction and the overproduction of reactive oxygen species (ROS). Sublethally stretched neurons produced surprisingly high levels of ROS, but these in isolation were insufficient to kill the cells. To be lethal, the ROS also needed to combine with nitric oxide (NO) to form the highly reactive species peroxynitrite. Peroxynitrite was not produced after stretch alone and arose only after combining stretch with an insult capable of stimulating NO production, such as NMDA or an NO donor. This explained the exquisite sensitivity of sublethally stretched neurons to a secondary NMDA insult. ROS scavengers and NO synthase (NOS) inhibitors prevented cell death and DNA degradation. Moreover, inhibiting neuronal NOS activation by NMDA using peptides that perturb NMDA receptor-postsynaptic density-95 interactions also reduced protein nitration and cell death, indicating that the reactive nitrogen species produced were neuronal in origin. Our data explain the mechanism of enhanced vulnerability of sublethally injured neurons to secondary excitotoxic insults and highlight the importance of secondary mechanisms to the ultimate outcome of neurons in mild neurotrauma.

The role of hydrogen peroxide in endothelial proliferative responses

Hydrogen peroxide (H2O2) is a recently recognized second messenger regulating proliferation in mammalian cells. Endothelial cells possess NADPH oxidases, which produce the H202 precursor superoxide (.O2-) in response to receptor-mediated signaling. Multiple physiologic agents have been shown to stimulate endothelial cells to produce .O2-/H2O2, including growth factors, such as vascular endothelial growth factor and transforming growth factor-beta1, and alterations in biomechanical forces, such as shear stress and cyclic strain. Downstream effects of these stimuli can often be inhibited by scavenging H2O2. Low concentrations of H2O2 stimulate proliferation or enhanced survival in a wide variety of cell types. Also, low concentrations of H2O2 stimulate endothelial migration as well as tube formation in an in vitro model of angiogenesis. Although low concentrations of H2O2 have been shown to be involved in numerous signal transduction pathways and to independently stimulate mitogenesis, there has been little information presented on precisely how mammalian cells respond biochemically to these low concentrations of H2O2. Recently a functional proteomics approach has been utilized to identify proteins responsive to low concentrations of H2O2 in human endothelial cells.

Rapid phosphorylation of heterogeneous nuclear ribonucleoprotein C1/C2 in response to physiologic levels of hydrogen peroxide in human endothelial cells

Hydrogen peroxide (H(2)O(2)) has been implicated as a signaling agent in numerous signal transduction pathways in mammalian cells. However, to date, no sensor for low concentrations (<10 microm) of H(2)O(2) has been identified. Using a functional proteomic approach, nuclear extracts from human umbilical vein endothelial cells were analyzed by two-dimensional PAGE with or without prior treatment with a low concentration of H(2)O(2). A protein doublet with a molecular mass of 39-41 kDa and a pI of approximately 5.0 was observed to be consistently altered by the treatment. Using proteolytic peptide mass fingerprinting, the protein was identified as heterogeneous nuclear ribonucleoprotein C1/C2, a nuclear restricted, pre-mRNA-binding protein. Upon two-dimensional PAGE, each heterogeneous nuclear ribonucleoprotein-C splice form was present as multiple spots because of differing levels of phosphorylation. Upon treatment with H(2)O(2), there was an increase in phosphorylation at 10-20 min, which partially reversed by 30 min. Subsequently, at 60 min after treatment, a population of unphosphorylated protein was transiently present. The effects were observed with as little as 1 microm H(2)O(2) and were maximal with 5-8 microm H(2)O(2). The H(2)O(2)-stimulated phosphorylation was inhibited by catalase, but not by the transcriptional inhibitor actinomycin D.

Intracellular generation of free radicals and modifications of detoxifying enzymes in cultured neurons from the developing rat forebrain in response to transient hypoxia

To address the influence of oxidative stress and defense capacities in the effects of transient hypoxia in the immature brain, the time course of reactive oxygen species generation was monitored by flow cytometry using dihydrorhodamine 123 and 2',7'-dichlorofluorescein-diacetate in cultured neurons issued from the fetal rat forebrain and subjected to hypoxia/reoxygenation (6 h/96 h). Parallel transcriptional and activity changes of superoxide dismutases, glutathione peroxidase and catalase were analyzed, in line with cell outcome. The study confirmed hypoxia-induced delayed apoptotic death, and depicted increased mitochondrial and cytosolic productions of free radicals (+30%) occurring over the 48-h period after the restoration of oxygen supply, with sequential stimulations of superoxide dismutases. Whereas catalase mRNA levels and activity were augmented by cell reoxygenation, glutathione peroxidase activity was transiently repressed (-24%), along with reduced glutathione reductase activity (-27%) and intracellular glutathione depletion (-19%). Coupled with the neuroprotective effects of the glutathione precursor N-acetyl-cysteine (50 microM), these data suggest that hypoxia/reoxygenation-induced production of reactive oxygen species can overwhelm glutathione-dependent antioxidant capacity, and thus may contribute to the resulting neuronal apoptosis.

Contribution of reactive oxygen species to 3-hydroxyglutarate neurotoxicity in primary neuronal cultures from chick embryo telencephalons

Glutaryl-CoA dehydrogenase deficiency is an autosomal recessively inherited neurometabolic disorder with a distinct neuropathology characterized by acute encephalopathic crises during a vulnerable period of brain development. 3-Hydroxyglutarate (3-OH-GA), which accumulates in affected patients, has been identified as an endogenous neurotoxin mediating excitotoxicity via N-methyl-D-aspartate receptors. As increased generation of reactive oxygen species (ROS) and nitric oxide (NO) plays an important role in excitotoxic neuronal damage, we investigated whether ROS and NO contribute to 3-OH-GA neurotoxicity. 3-OH-GA increased mitochondrial ROS generation in primary neuronal cultures from chick embryo telencephalons, which could be prevented by MK-801, confirming the central role of N-methyl-D-aspartate receptor stimulation in 3-OH-GA toxicity. ROS increase was reduced by alpha-tocopherol and--less effectively-by melatonin. alpha-Tocopherol revealed a wider time frame for neuroprotection than melatonin. Creatine also reduced neuronal damage and ROS formation but only if it was administered >or=6 h before 3-OH-GA. NO production revealed only a slight increase after 3-OH-GA incubation. NO synthase inhibitor N(omega)-nitro-L-arginine prevented NO increase but did not protect neurons against 3-OH-GA. The NO donor S-nitroso-N-acetylpenicillamine revealed no effect on 3-OH-GA toxicity at low concentrations (0.5-5 microM), whereas it potentiated neuronal damage at high concentrations (50-500 microM), suggesting that weak endogenous NO production elicited by 3-OH-GA did not affect neuronal viability. We conclude from our results that ROS generation contributes to 3-OH-GA neurotoxicity in vitro and that radical scavenging and stabilization of brain energy metabolism by creatine are hopeful new strategies in glutaryl-CoA dehydrogenase deficiency.

Light-dependent generation of reactive oxygen species in cell culture media

Cell culture media (RPMI 1640, Dulbecco's Minimal Essential Medium and yeast extract-peptone-glucose medium) were found to oxidize dichlorodihydrofluorescein diacetate and dihydrorhodamine 123, and to generate spin adduct of 5,5'-dimethyl-1-pyrroline N-oxide, which indicates formation of reactive oxygen species (ROS). The production of ROS was light dependent. The main component of the media responsible for the generation of ROS was riboflavin, but tryptophan, tyrosine, pyridoxine, and folic acid enhanced the effect of riboflavin. These observations point to exposure of cells to ROS under in vitro culture conditions.

Free radical production and changes in superoxide dismutases associated with hypoxia/reoxygenation-induced apoptosis of embryonic rat forebrain neurons in culture

Following hypoxia/reoxygenation (6h/96h), cultured neurons from the embryonic rat forebrain undergo delayed apoptosis. To evaluate the participation of oxidative stress and defense mechanisms, temporal evolution of intraneuronal free radical generation was monitored by flow cytometry using dihydrorhodamine 123, in parallel with the study of transcriptional, translational, and activity changes of the detoxifying enzymes Cu/Zn-SOD and Mn-SOD. Two distinct peaks of radical generation were depicted, at the time of reoxygenation (+ 27%) and 48 h later (+ 25%), respectively. Radical production was unaffected by caspase inhibitors YVAD-CHO or DEVD-CHO, which prevented neuronal damage, suggesting that caspase activation is not an upstream initiator of radicals in this model. Cell treatment by vitamin E (100 microM) displayed significant neuroprotection, whereas the superoxide generating system xanthine/xanthine oxidase induced apoptosis. Transcript and protein levels of both SODs were reduced 1 h after the onset of hypoxia, but activities were transiently stimulated. Reoxygenation was associated with an increased expression (139%), but a decreased activity (21%) of the inducible Mn-SOD, whereas Cu/Zn-SOD protein and activity were low and progressively increased until 48 h post-hypoxia, when the second rise in radicals occurred. In spite of a temporal regulation of SODs, which parallels radical formation, oxidative stress might account for neurotoxicity induced by hypoxia.

Screening of new antioxidant molecules using flow cytometry

We present a flow cytometry technique to evaluate the antioxidative properties of molecules on living cells, using a stable murine-murine hybridoma (Mark 3) cell line routinely cultured. Using this technique, intracellular superoxide anions and peroxides were evaluated with dihydrorhodamine (DHR-123) and dichlorofluorescein diacetate (DCFH-DA), respectively. When cells were first incubated for 10 min with either H(2)O(2) or the xanthine (X)/xanthine oxidase (XO) system, this flow cytometric technique was capable of evaluating the oxidative stress on cells. Twenty-one new analogues of ellipticine were synthesized and tested for their antioxidative properties compared to vitamin E and Ebselen used as references. A good statistical reflection of the antioxidative activities of these molecules was achieved by analyzing 35 000 cells in each experiment. Among them, the selenated molecule 18 was found to be 10 times more active than Ebselen but 10 000 times less active than vitamin E. Moreover, eight compounds showed glutathione peroxidase-like activities.

Bovine beta-lactoglobulin receptors on transformed mammalian cells (hybridomas MARK-3): characterization by flow cytometry

Flow cytometry was used to demonstrate the presence of beta-lactoglobulin (betaLG) receptors on living murine hybridoma MARK-3 cells using a fluorescein isothiocyanate-betaLG conjugate (FITC-betaLG: molar ratio of 5:1). A site occupation curve was produced using a shift in the mean channel fluorescence at various concentrations of FITC-betaLG. The binding of labelled ligand was concentration dependent and was inhibited by unlabelled betaLG. The on-rate constant was 3.2x10(2) M(-1) min(-1) and the off-rate constant was 0.002 min(-1). Scatchard plot analysis gave a dissociation constant (K(d)) of 44+/-21x10(-7) and 39+/-24x10(-5) M (n=3). Flow cytometry indicated that at least 15% of the FITC-betaLG were internalized for 5 min and that internalization was temperature- and time-dependent. The internalization was confirmed by 3-D fluorescence microscopy (CELLScan system).

Concentration dependent effects of hydrogen peroxide on lens epithelial cells

AIMS

To evaluate the effects of hydrogen peroxide exposure on the survival and proliferation of cultured lens epithelial cells.

METHODS

TOTL-86 cells, a line of rabbit lens epithelial cells, were used. The survival and proliferation of TOTL-86 cells were quantified by a rapid colorimetric assay (MTT assay). To determine the effects of hydrogen peroxide, TOTL-86 cells were exposed to different concentrations of hydrogen peroxide. To determine the effect of cell numbers on the survival and proliferation of TOTL-86 cells at a fixed concentration of hydrogen peroxide, different numbers of cells were plated and exposed to hydrogen peroxide. To determine whether there is a synergistic effect between hydrogen peroxide and EGF, bFGF, PDGF-AA, and insulin, TOTL-86 cells were exposed to hydrogen peroxide combined with one of these growth factors.

RESULTS

High levels (1 mM) of hydrogen peroxide killed TOTL-86 cells and sublethal levels (100 microM) suppressed their proliferation. From 1 nM to 1 microM of hydrogen peroxide, there was a dose dependent increase in the cell numbers. The initial seeded cell number dramatically affected the response to hydrogen peroxide. Although growth factors showed no synergistic effects with hydrogen peroxide on proliferation, both EGF and insulin, but not bFGF or PDGF, rescued TOTL-86 cells from the sublethal effect.

CONCLUSION

Hydrogen peroxide in cooperation with some growth factors plays an important role in the proliferation of lens epithelial cell.

Effect of the 21-aminosteroid U74389G on oxygen-induced free radical production, lipid peroxidation, and inhibition of lung growth in neonatal rats

Bronchopulmonary dysplasia is a chronic pneumopathy of preterm infants, with significant associated mortality and morbidity, for which there is no effective preventive therapy. Pulmonary O2 toxicity is thought to be a major contributor to the development of bronchopulmonary dysplasia, and antioxidant interventions hold significant promise for therapy. The relative importance of specific reactive oxygen species in the development of O2-mediated lung injury is unknown. In this study, we tested the effect of a synthetic 21-aminosteroid, U74389G, on 95% O2-induced free radical production, lipid peroxidation, and inhibition of postnatal lung growth in a neonatal rat model. Lipid peroxidation products, as measured by total 8-isoprostane and aldehydes, and hydroxyl radical formation, assessed using salicylate metabolites, in rat lungs and serum were significantly increased after exposure to 95% O2. These changes could be completely or partially attenuated by U74389G. However, U74389G did not improve the survival rate or lung wet-to-dry weight ratio. Expression of proliferating cell nuclear antigen, a marker for DNA synthesis, was examined by immunohistochemistry. Four- or 7-d-old control rat lungs had active DNA synthesis, which was inhibited by exposure to 95% O2. U74389G had a protective effect against 95% O2-mediated inhibition of DNA synthesis. Air-exposed animals treated with U74389G had a modest reduction in lung DNA synthesis, consistent with a role for hydroxyl radicals or lipid hydroperoxides as second messengers in the normal regulation of lung growth.