Intracellular calcium homeostasis during hydrogen peroxide injury to cultured P388D1 cells

Hydrogen peroxide sensor HPCA1 is an LRR receptor kinase in Arabidopsis

Hydrogen peroxide (H₂O₂) is a major reactive oxygen species in unicellular and multicellular organisms, and is produced extracellularly in response to external stresses and internal cues^1-4. H₂O₂ enters cells through aquaporin membrane proteins and covalently modifies cytoplasmic proteins to regulate signalling and cellular processes. However, whether sensors for H₂O₂ also exist on the cell surface remains unknown. In plant cells, H₂O₂ triggers an influx of Ca²⁺ ions, which is thought to be involved in H₂O₂ sensing and signalling. Here, by using forward genetic screens based on Ca²⁺ imaging, we isolated hydrogen-peroxide-induced Ca²⁺ increases (hpca) mutants in Arabidopsis, and identified HPCA1 as a leucine-rich-repeat receptor kinase belonging to a previously uncharacterized subfamily that features two extra pairs of cysteine residues in the extracellular domain. HPCA1 is localized to the plasma membrane and is activated by H₂O₂ via covalent modification of extracellular cysteine residues, which leads to autophosphorylation of HPCA1. HPCA1 mediates H₂O₂-induced activation of Ca²⁺ channels in guard cells and is required for stomatal closure. Our findings help to identify how the perception of extracellular H₂O₂ is integrated with responses to various external stresses and internal cues in plants, and have implications for the design of crops with enhanced fitness.

Neuroprotective activity of galloylated cyanogenic glucosides and hydrolysable tannins isolated from leaves of Phyllagathis rotundifolia

The galloylated cyanogenic glucosides based on prunasin (1-7), gallotannins (8-14), ellagitannins (15-17), ellagic acid derivatives (18, 19) and gallic acid (20) isolated from the leaves of Phyllagathis rotundifolia (Melastomataceae) were investigated for their neuroprotective activity against hydrogen peroxide (H(2)O(2))-induced oxidative damage in NG108-15 hybridoma cell line. Among these compounds, the gallotannins and ellagitannins exhibited remarkable neuroprotective activities against oxidative damage in vitro as compared to galloylated cyanogenic glucosides and ellagic acid derivatives in a dose-dependent manner. They could be explored further as potential natural neuroprotectors in various remedies of neurodegenerative diseases.

Pathophysiologically relevant levels of hydrogen peroxide induce glutamate-independent neurodegeneration that involves activation of transient receptor potential melastatin 7 channels

Stroke/brain ischemia is a leading cause of death and long-term disabilities. Increased oxidative stress plays an important role in the pathology of brain ischemia. Hydrogen peroxide (H(2)O(2)) is a major oxidant known to cause neuronal injury; however, the detailed mechanism remains unclear. Previous studies have suggested that H(2)O(2)-induced injury is associated with increased intracellular Ca(2+), mediated by glutamate receptors or voltage-gated Ca(2+) channels. Here, we demonstrate that, at concentrations relevant to stroke, H(2)O(2) induces a Ca(2+)-dependent injury of mouse cortical neurons in the absence of activation of these receptors/channels. With the culture medium containing blockers of glutamate receptors and voltage-gated Ca(2+) channels, brief exposure of neurons to H(2)O(2) induced a dose-dependent injury. Reducing [Ca(2+)](e) inhibited whereas increasing [Ca(2+)](e) potentiated the H(2)O(2) injury. Fluorescent Ca(2+) imaging confirmed the increase of [Ca(2+)](i) by H(2)O(2) in the presence of the blockers of glutamate receptors and voltage-gated Ca(2+) channels. Addition of 2-aminoethoxydiphenyl borate, an inhibitor of transient receptor potential melastatin 7 (TRPM7) channels, or the use of TRPM7-small interference RNA, protected the neurons from H(2)O(2) injury. In contrast, overexpressing TRPM7 channels in human embryonic kidney 293 cells increased H(2)O(2) injury. Our findings indicate that H(2)O(2) can induce Ca(2+) toxicity independent of glutamate receptors and voltage-gated Ca(2+) channels. Activation of TRPM7 channels is involved in such toxicity.

Multiple mechanisms for hydrogen peroxide-induced apoptosis

The mechanisms of cell killing by oxidative stress, in particular by hydrogen peroxide, are not yet well clarified. Here, we show that during recovery after H(2)O(2) treatment, apoptosis occurs in two different waves, peaking at 8 h (early) and 18 h (late) of recovery from oxidative stress. The two peaks are differentially modulated by a set of inhibitors of metabolic processes, which suggests that the first peak depends on DNA break formation, whereas the second may be correlated with H(2)O(2)-induced mitochondrial alterations.

Activation of the calcium/calmodulin-dependent protein kinases as a consequence of oxidative stress

Oxygen radicals have diverse effects on cells. In many cases, exposure to reactive oxygen intermediates (ROI) can induce cell death. Conversely, there is also evidence that suggests oxygen radicals can activate signaling pathways that are thought to prevent cell death. In this review, the authors discuss the finding that hydrogen peroxide and ROI-generating treatments trigger the activation of the calcium/calmodulin-dependent kinases (CaM-kinases), and the potential role this activation has in preventing apoptosis. Evidence is presented that CaM-kinase activation occurs by both calcium dependent- and independent-pathways in response to ROIs. In addition, the idea is discussed that ROIs have the potential to lead to the phosphorylation of calmodulin and through this mechanism potentiate the activation of the CaM-kinases. The concept that inhibition of the CaM-kinases as a mechanism to sensitize cells to the damaging effects of ROIs is also presented. Contrasting these studies, evidence is presented that exposure of the CaM-kinases directly to hydrogen peroxide also has the apparent ability to inhibit their activity.

Antioxidative and neuroprotective activities of extracts from the fruit hull of mangosteen (Garcinia mangostana Linn.)

OBJECTIVE

The aim of this study was to investigate the antioxidative and neuroprotective activities of various extracts from the fruit hull of mangosteen (Garcinia mangostana Linn., GM).

MATERIALS AND METHODS

Four extracts: water, 50% ethanol, 95% ethanol and ethyl acetate, were used. The antioxidative activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl free-radical scavenging assay at extract concentrations of 1, 10, 50 and 100 microg/ml. Based on the free radical scavenging activity of the extracts, two (water and 50% ethanol) were selected for their protective activity in NG108-15 neuroblastoma cells against H(2)O(2)-induced oxidative stress and for cell viability using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

RESULTS

All extracts exhibited antioxidative activity. The water and 50% ethanol extracts showed high free-radical scavenging activity with IC(50) values of 34.98 +/- 2.24 and 30.76 +/- 1.66 microg/ml, respectively. Both water and 50% ethanol extracts exhibited neuroprotective activity on NG108-15 cells. The highest activity was observed at the concentration of 50 microg/ml for both the water and 50% ethanol extracts. For cytotoxicity test, none of the extracts was toxic to the cells except at the high concentration of 100 microg/ml.

CONCLUSIONS

These results suggest that the water and 50% ethanol extracts from the fruit hull of GM may be potent neuroprotectants.

Survival pathways triggered by peroxynitrite in cells belonging to the monocyte/macrophage lineage

Peroxynitrite, a highly reactive nitrogen species, promotes in U937 cells (a promonocytic cell line) a mitochondrial permeability transition (MPT)-dependent necrosis. An initial event triggered by peroxynitrite (i.e., inhibition of complex III of the mitochondrial respiratory chain) is responsible for the time-dependent formation of H(2)O(2), essential for the occurrence of cell death. Otherwise non-toxic concentrations of peroxynitrite nevertheless commit cells to MPT-dependent necrosis, which is however prevented by a cytoprotective signaling driven by arachidonic acid (AA) released by the cytosolic PLA(2) isoform. Interestingly, the mechanism whereby delayed formation of H(2)O(2) promotes toxicity in cells exposed to intrinsically toxic concentrations of peroxynitrite is independent of the accumulation of additional damage. Cell death is in fact mediated by inhibition of the AA-dependent cytoprotective signaling. Exogenous AA, however, prevented toxicity also under these conditions. An additional point to be made is that the major findings obtained using U937 cells were reproduced in different cell types belonging to the monocyte/macrophage lineage. Hence, within the context of the inflammatory response, monocytes and macrophages may cope with peroxynitrite by using AA, a signaling molecule largely available at the inflammatory sites.

Cremophor EL, a non-ionic surfactant, promotes Ca2+-dependent process of cell death in rat thymocytes

Cremophor EL, a surfactant for pharmaceutical products, augments the cytotoxicity of hydrogen peroxide in rat thymocytes [Iwase, K., Oyama, Y., Tatsuishi, T., Yamaguchi1, J., Nishimura1, Y., Kanada, A., Kobayashi, M., Maemura, Y., Ishida, S., Okano, Y., 2004. Cremophor EL augments the cytotoxicity of hydrogen peroxide in lymphocytes dissociated from rat thymus glands. Toxicol. Lett. 154, 143-148]. The effect of cremophor EL on Ca(2+)-dependent process of cell death has been examined using a flow cytometer since hydrogen peroxide increases intracellular Ca2+ concentration. Cremophor EL at clinically-relevant concentrations greatly increased the population of dead cells in rat thymocytes simultaneously treated with A23187, a calcium ionophore increasing intracellular Ca2+ concentration. Removal of Ca2+ from external solution diminished the cremophor EL-induced increase in the dead cell population. Result suggests that Ca(2+)-dependent process is involved in the cremophor EL-induced decrease in the cell viability in the simultaneous presence of A23187. The population of cells with hypodiploidal DNA was not increased by the application of cremophor EL and A23187 although the cell viability was greatly decreased, indicating that the type of cell death is necrosis. It is suggested that cremophor EL at clinically-relevant concentrations augments the Ca(2+)-dependent process of necrosis.

Effects of hydrogen peroxide on sodium current in acutely isolated rat hippocampal CA1 neurons

The effects of hydrogen peroxide (H2O2) on sodium currents (Na+ currents) in freshly dissociated rat hippocampal neurons were studied using the whole-cell patch-clamp techniques. H2O2 caused a reversible increase of the voltage-activated Na+ currents in a concentration- and voltage-dependent manner. The half-increasing concentration (EC50) of H2O2 on Na+ currents was 10.79 microM. In addition, 10 microM H2O2 shifted the steady-state inactivation curve of Na+ currents toward positive potential (control Vh = -64.58 +/- 1.22 mV, H2O2 Vh = -53.55 +/- 0.94 mV, n = 10, P < 0.01 without changing the slope factor). However, the steady-state activation curve was not affected. These results indicated that H2O2 could increase the amplitudes of Na+ currents and change the inactivation properties of Na+ channels even in very low concentration.

Antioxidant and Free Radical-Scavenging Activity of Choto-san and Its Related Constituents

The antioxidant properties of Choto-san and its related constituents such as Chotoko and Choto-san without Chotoko, and phenolic compounds contained in Chotoko such as epicatechin, caffeic, acid and quercetin were evaluated. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging assay, the scavenging activity of Chotoko (IC(50) 14.3 microg/ml) was found to be higher than that of Choto-san (IC(50) 206.2 microg/ml) and Choto-san without Chotoko (IC(50) 244.3 microg/ml). Epicatechin (IC(50) 10.4 microM), caffeic acid (IC(50) 13.8 microM), and quercetin (IC(50) 7.1 microM) also revealed scavenging activity against DPPH radicals. Choto-san (IC(50) 67.7 microg/ml) exhibited stronger inhibitory activity against superoxide anion formation than Choto-san without Chotoko (IC(50) 92.4 microg/ml) but weaker activity than Chotoko (IC(50) 18.3 microg/ml). The generation of superoxide anion was also inhibited by epicatechin (IC(50) 175.2 microM), caffeic acid (IC(50) 141.7 microM), and quercetin (IC(50) 18.7 microM). In a hydroxyl radical-scavenging experiment, Choto-san (IC(50) 2.4 mg/ml), Chotoko (IC(50) 2.2 mg/ml), Choto-san without Chotoko (IC(50) 2.8 mg/ml), epicatechin (IC(50) 3.9 mM), caffeic acid (IC(50) 3.6 mM), and quercetin (IC(50) 1.9 mM) exhibited activity. In NG108-15 cells, when added simultaneously with H(2)O(2) (500 microM), Choto-san (250 microg/ml), Chotoko (250 microg/ml), Choto-san without Chotoko (500 microg/ml), epicatechin (200 microM), caffeic acid (200 microM), and quercetin (200 microM) effectively protected cells from oxidative damage. In conclusion, the present results provide evidence that Choto-san acts as an antioxidant and cytoprotective agent against oxidative damage, which is due at least partly to the phenolic compounds contained in Chotoko.

Cytoprotective and cytotoxic effects of curcumin: dual action on H2O2-induced oxidative cell damage in NG108-15 cells

The ability of curcumin, a natural antioxidant isolated from Curcuma longa, to inhibit hydrogen peroxide (H(2)O(2))-induced cell damage in NG108-15 cells was examined. When added simultaneously with 500 microM H(2)O(2), curcumin (25-100 microM) effectively protected cells from oxidative damage. However, when the cells were pretreated with curcumin (25-100 microM) for 1.5 h before H(2)O(2) exposure, curcumin was unable to inhibit H(2)O(2)-induced cell damage. Instead, it caused a significant concentration-dependent decrease in cell viability after H(2)O(2) exposure. This dual action of curcumin suggests that pretreatment with curcumin by itself did not have any significant effect on the viability of the NG108-15 cells, but it sensitized them to oxidative damage induced by H(2)O(2) under our experimental conditions. It appears that these events may not relate to the antioxidant and free radical scavenging activities of curcumin.

Possible underlying mechanism for hydrogen peroxide-induced electromechanical suppression in human atrial myocardium

Hydrogen peroxide (H(2)O(2)) and its metabolites have been shown to exert complex effects on the cardiac muscle during cardiac ischemia/reperfusion. The aim of the present study, by perfusing H(2)O(2) or/and different scavengers of oxygen free radicals (OFRs) into the human atrium, is to characterize the electropharmacological effects of H(2)O(2) and explore its possible underlying mechanism. Atrial tissues obtained from the heart of 19 patients undergoing corrective cardiac surgery were used. Transmembrane action potentials were recorded using the conventional microelectrode technique, and contraction of atrial fibers was evaluated in normal [K](o) (4 mM) in the absence and presence of tested agents. H(2)O(2) (30 micro M-3 mM) had a biphasic effect on the contractile force (an increase, followed by a decrease), reduced the 0-phase depolarizing slope (dV/dt), and prolonged the action potential duration (APD) in a concentration-dependent manner. However, even at a concentration as high as 3 mM, H(2)O(2) did not influence diastolic membrane potential (DMP). Pretreatment with N-(mercaptopropionyl)-glycine (N-MPG), a specific scavenger of the. OH free radical, significantly blocked the 3 mM H(2)O(2)-induced electromechanical changes, while the pretreatment with L-methionine (L-M), a specific scavenger of HOCl free radical, did not. Our data suggests that the toxic effects of H(2)O(2) are caused mainly through the generation of. OH, which is attributed to the electropharmacological inhibitory effects seen in the human atrium.

Protective effect of ginkgo biloba extract on endothelial cell against damage induced by oxidative stress

The viability of bovine aortic endothelial cells (BAECs) treated with 0.1 m H O was decreased by 39.8%, and 100 mg/l EGb761 increased the viability by 20.6%. Exposure BAECs to H O for 6 min resulted in a significant elevation in the intracellular free Ca. Pretreatment of BAECs with 10 mg/l and 100 mg/l EGb761 for 10 min showed a decrease in the intracellular free Ca, 4.5% and 20.6%, respectively. The apoptotic rate of BAECs measured by propidium iodide (PI) staining was (38.1 +/- 2%) after 18 h of treatment with H O. Pretreatment of BAECs with 100 mg/l EGb761 for 1 h reduced the apoptotic rate to 27 +/- 1%. In addition, there were about 5-7% of cells stained positive measured by TUNEL assay. When BAECs were exposed to 0.1 m H O for 18 h, the number of TUNEL-positive cells increased to 37-44%. When 10 mg/l EGb761 and 100 mg/l EGb761 were used, the TUNEL-positive cells decreased to 26.5 +/- 3.1% and 17.5 +/- 1.7%, respectively. Furthermore, EGb761 also inhibited caspase-3 activity induced by H O. It is concluded that EGb761 has protective effect on bovine vascular endothelial cells against damage induced by H O. Further studies are needed to clarify the mechanisms of action of EGb761.

Higher order chromatin degradation: implications for neurodegeneration

Higher order chromatin degradation (HOCD) is a hallmark of programmed cell death. HOCD is mediated by enzymatic digestion of the DNA backbone at matrix attachment regions, and ultimately results in the excision of chromatin loops and their oligomers from chromosomes. We have recently demonstrated that hydrogen peroxide (H2O2), the major mediator of oxidative stress, rapidly induces HOCD. This demonstration allowed us to characterize several kinetic features of HOCD. Moreover, H2O2-induced HOCD provides a mechanistic link between oxidative stress and the pathology of neurodegeneration. Thus, in acute neurodegenerative conditions, which feature severe oxidative stress, H2O2-induced HOCD efficiently dismantles the genome, and thus, irreversibly commits cells to death. In chronic neurodegenerative conditions, which feature sublethal but perennial oxidative stress, cells undergo only a partial fragmentation of the genome via H2O2-induced HOCD. If unrepaired of improperly repaired, such a partial fragmentation leads to the generation and accumulation of somatic mutations that are likely to play the key role in delayed degeneration and death of neural cells.

Higher order chromatin degradation in glial cells: the role of calcium

Higher order chromatin degradation (HOCD), i.e. the scission of nuclear chromatin loops at the matrix attachment regions (MARs), is a hallmark of programmed cell death. We have previously demonstrated that hydrogen peroxide (H(2)O(2)) induces rapid HOCD in cultured oligodendrocytes generating two subpopulations of DNA fragments of >or=400 and 50-200 kb. In the present study, we examined the involvement of calcium in this process. HOCD was induced in primary rat oligodendrocytes by exposure to 1 mM H(2)O(2) and assessed by field inversion gel electrophoresis with and without S1 endonuclease digestion, to detect single and double stranded fragmentation, respectively. Chelating intracellular calcium with BAPTA/AM prior to H(2)O(2) exposure inhibited HOCD in a dose-dependent manner. Complete inhibition of HOCD was attained with 50 muM BAPTA/AM. The pretreatment of cells with desferroxamine mesylate, which may lower intracellular calcium levels, also resulted in a profound inhibition of HOCD, but the initial chromatin digestion into >or=400 kb single stranded DNA fragments was unaffected. Neither removing extracellular calcium nor blocking calcium release from intracellular stores with TMB-8 affected HOCD. Moreover, increasing intracellular calcium with A23187 calcium ionophore did not induce HOCD. Subsequent study in nuclei purified from C6 glioma cells revealed that the endonuclease responsible for HOCD is calcium-independent, but is magnesium-dependent. Magnesium-induced HOCD was not affected by the removal of calcium from nuclei with EGTA, but was practically abrogated in nuclei prepared from BAPTA/AM-pretreated cells. These results indicate that although H(2)O(2)-induced HOCD is not directly mediated by an increase of intracellular calcium concentration, normal resting levels of intracellular calcium are required for the maintenance of MAR-associated endonuclease in an active form.

H2O2-induced block of glycolysis as an active ADP-ribosylation reaction protecting cells from apoptosis

H2O2 treatment on U937 cells leads to the block of glycolytic flux and the inactivation of glyceraldehyde-3-phosphate-dehydrogenase by a posttranslational modification (possibly ADP-ribosylation). Glycolysis spontaneously reactivates after 2 h of recovery from oxidative stress; thereafter cells begin to undergo apoptosis. The specific ADP-ribosylation inhibitor 3-aminobenzamide inhibits the stress-induced inactivation of glyceraldehyde-3-phosphate-dehydrogenase and the block of glycolysis; concomitantly, it anticipates and increases apoptosis. Exogenous block of glycolysis (i.e., by culture in glucose-free medium or with glucose analogs or after NAD depletion), turns the transient block into a stable one: this results in protection from apoptosis, even when downstream cell metabolism is kept active by the addition of pyruvate. All this evidence indicates that the stress-induced block of glycolysis is not the result of a passive oxidative damage, but rather an active cell reaction programmed via ADP-ribosylation for cell self-defense.

Effect of hydrogen peroxide on the membrane currents of sinoatrial node cells from rabbit heart

The effects of H(2)O(2) on pacemaker activity and underlying membrane currents were studied in isolated rabbit sinoatrial (SA) node cells using perforated patch current- and voltage-clamp methods. Short-term exposure (<10 min) of the nodal cells to H(2)O(2) (200 microM) resulted in an initial shortening of spontaneous action potential cycle length (from 445 +/- 60 to 398 +/- 56 ms; P < 0.05) and a prolongation of action potential duration. H(2)O(2) (100 microM) significantly increased peak L-type Ca(2+) current (I(Ca,L)) from -384 +/- 77 to -439 +/- 84 pA (116 +/- 2%, n = 6). Additionally, the persistent or non-inactivating component of I(Ca,L) was increased from -52 +/- 3 to -88 +/- 14 pA (174 +/- 19%, n = 6). The hyperpolarization-activated current (I(f)) was decreased from -228 +/- 62 to -161 +/- 72 pA after exposure to H(2)O(2) (n = 7). There were no changes in the delayed rectifier K(+) current (I(K)) (n = 7). H(2)O(2)-induced Ca(2+) currents were blocked by 2 microM nicardipine (n = 6), 2 mM Ni(2+) (n = 2), and the protein kinase C (PKC) inhibitor bisindolylmaleimide (10(-7) M; n = 4) but not by 20 microM tetrodotoxin. These results suggest that H(2)O(2) can increase the spontaneous pacing rate in rabbit SA node cells by enhancing I(Ca,L) and that this effect is mediated by a PKC-dependent pathway.

Calcium associated resistance to H(2)O(2) in Chinese hamster V79 cells

To investigate whether the difference in cellular sensitivity of Chinese hamster V79 and their H(2)O(2)-resistant variant cells (Hpr-4) to H(2)O(2) relates to the difference in intracellular Ca(2+) concentration in these cells, we measured Ca(2+) concentration by calcium ion analysis after loading these cells with Fura-2/AM. Intracellular Ca(2+) concentration increased in both Chinese hamster V79 and Hpr-4 cells as extracellular Ca(2+) concentration increased. However, the increase in intracellular Ca(2+) concentration in response to extracellular H(2)O(2) was more pronounced in Hpr-4 than V79 cells. H(2)O(2) cytotoxicity of Hpr-4 but not V79 cells was also decreased in response to the increase in extracellular Ca(2+) concentration. In parallel with the decrease in cytotoxicity in response to increasing extracellular Ca(2+) concentration, the frequency of mitochondrial DNA single strand breaks (SSB) in Hpr-4 cells also decreased without producing observable nuclear DNA SSB. Use of permeabilized V79 and Hpr-4 cells exposed to H(2)O(2) showed that mitochondrial DNA SSB decreased when extramitochondrial Ca(2+) concentration increased. These findings indicate that elevated intracellular Ca(2+) concentration may protect against H(2)O(2)-induced mitochondrial damage and cytotoxicity in these cells.

In vitro effects of hydrogen peroxide on the cochlear neurosensory epithelium of the guinea pig

Reactive oxygen species (ROS) have been postulated to be involved in drug ototoxicity and noise-induced hearing loss. Hydrogen peroxide (H(2)O(2))-induced cell damage in the inner ear was investigated using the neurosensory epithelium of a guinea pig cochlea. Hair cells and supporting cells of the epithelium incubated in Hanks' balanced salt solution were viable up to 6 h. After 2 h of treatment with 0.2 mM H(2)O(2) about 85% of the outer hair cells lost their viability. In contrast inner hair cells slowly began to die after 2 h of H(2)O(2) treatment. The Deiters cells and Hensen cells did not show any signs of damage in the presence of H(2)O(2). Nifedipine, a calcium channel blocker, Quin-2 AM, an intracellular calcium chelator, and 2,2'-dipyridyl, a membrane-permeable iron chelator, all provided partial protection against H(2)O(2)-induced outer hair cell death. The combination of both chelators showed an additional protective effect. The antioxidants N-acetylcysteine and glutathione-monoethyl ester completely protected against H(2)O(2) damage. These results suggest that calcium, iron, and thiol homeostasis play a crucial role in hair cell death caused by H(2)O(2).

Exposure of rat thymocytes to hydrogen peroxide increases annexin V binding to membranes: inhibitory actions of deferoxamine and quercetin

Effects of hydrogen peroxide (H(2)O(2)) on rat thymocytes were examined, using a flow cytometer and three fluorescent probes, annexin V-fluorescein isothiocyanate (annexin V-FITC) for detecting phosphatidylserine expressed on the membrane surface, ethidium bromide for estimating dead cells, and fluo-3-acetoxymethyl ester (fluo-3-AM) for monitoring changes in intracellular Ca(2+) concentration ([Ca(2+)](i)), to characterize H(2)O(2)-induced cytotoxicity. Exposure to H(2)O(2) (30 microM or more) increased the number of annexin V-positive live cells dose- and time-dependently while the number of dead cells increased at concentrations of 1 mM or more. H(2)O(2) (30 microM or more) increased [Ca(2+)](i) in a dose-dependent manner. Threshold concentration of H(2)O(2) to increase [Ca(2+)](i) was similar to that to increase annexin V binding to membranes. The H(2)O(2)-induced change in cell membranes was attenuated under Ca(2+)-free conditions. Therefore, it is likely that Ca(2+) is involved in the H(2)O(2)-induced cytotoxicity. Deferoxamine was effective to protect the cells suffering from H(2)O(2)-induced oxidative stress, suggesting a contribution of hydroxyl radicals generated by the Fenton reaction. Quercetin also exerted a potent protective action on cells suffering from H(2)O(2)-induced oxidative stress. The results indicate that the exposure of rat thymocytes to H(2)O(2) at micromolar concentrations increases annexin V binding to cell membranes in a Ca(2+)-dependent manner, suggesting the possibility that the oxidative stress caused by H(2)O(2) (and/or hydroxyl radicals) induces apoptosis via increasing [Ca(2+)](i).

Characterization of reactive oxygen species induced effects on human spermatozoa movement and energy metabolism

Reactive oxygen species (ROS) inhibit sperm movement and have been implicated in male infertility. In this study, we determined the effects of specific ROS produced by activated leukocytes on human spermatozoa and investigated their metabolic site of action. We used chemiluminescence and electron paramagnetic resonance (EPR) to characterize the ROS generated by both blood and seminal leukocytes. We also determined the effects of these ROS on sperm energy metabolism using biochemical analyses and flow cytometry. Both blood and seminal leukocytes produced the same characteristic ROS which were determined to be hydrogen peroxide (H2O2) and superoxide radicals (O2*-). EPR using the spin trapping technique indicated that superoxide radical-dependent hydroxyl radicals (HO.) were also generated. ROS generated by PMA-stimulated blood leukocytes (2-5 x 10(6)/ml) caused inhibition of sperm movement in 2 h (p < .01). Using the hypoxanthine/ xanthine oxidase (0.5 U/ml) system to generate ROS, we determined that spermatozoa ATP levels, after ROS treatment, were reduced approximately eight-fold in 30 min (0.10 x 10(10) moles/10(6) sperm cells) compared to control (0.84 X 10(-10) moles/10(6) sperm cells) (p < .01). Sperm ATP reduction paralleled the inhibition of sperm forward progression. Neither superoxide dismutase (100 U/ml) nor dimethyl sulfoxide (100 mM) reversed these effects; however, protection was observed with catalase (4 X 10(3) U/ml). Flow cytometric analyses of sperm treated with various doses of H2O2 (0.3 mM-20.0 mM) showed a dose-dependent decrease in sperm mitochondrial membrane potential (MMP); however, at low concentrations of H2O2, sperm MMP was not significantly inhibited. Also, sperm MMP uncoupling with CCClP had no effect on either sperm ATP levels or forward progression. These results indicate that H2O2 is the toxic ROS produced by activated leukocytes causing the inhibition of both sperm movement and ATP production. O2*- and HO. do not play a significant role in these processes. Low concentrations of H2O2 causing complete inhibition of sperm movement and ATP levels inhibit sperm energy metabolism at a site independent of mitochondrial oxidative phosphorylation.

Stimulation of active sodium-potassium transport by hydrogen peroxide in cultured rabbit nonpigmented ciliary epithelium

PURPOSE

Studies were conducted to examine the effect of hydrogen peroxide on active sodium-potassium transport in a cell line derived from nonpigmented ciliary epithelium of the rabbit eye.

METHODS

Studies were carried out using a rabbit nonpigmented ciliary epithelium cell line. 86Rb uptake by intact cells was measured in the presence or absence of ouabain. The ouabain-sensitive potassium (86Rb) uptake rate was used as an index of the rate of active sodium-potassium transport. Cell sodium content was measured by atomic absorption spectrophotometry. Na,K-ATPase activity was determined by measuring ATP hydrolysis in the presence or absence of ouabain, using membrane material isolated by centrifugation of cell homogenates.

RESULTS

Ouabain-sensitive potassium (86Rb) uptake rate measured in cells that had been preincubated with 200microM hydrogen peroxide for either 30 min or 60 min was increased to 196% and 181% of the control uptake rate, respectively. Lesser concentrations of hydrogen peroxide caused lesser degrees of stimulation. 200microM hydrogen peroxide caused an increase of cell sodium content. Such a change of cell sodium content is likely to be responsible, at least in part, for the observed stimulation of active sodium-potassium transport. However, the response may also be partly dependent on activation of a protein kinase since the serine/threonine protein kinase inhibitors staurosporine (1microM) and H-89 (20microM) were both found to prevent the stimulatory effect of 200microM hydrogen peroxide on ouabain-sensitive potassium (86Rb) uptake. Interestingly, neither H-89 nor staurosporine prevented the elevation of sodium content in cells that received 200microM hydrogen peroxide.

CONCLUSIONS

Taken together, these findings suggest a low concentration of hydrogen peroxide causes increased sodium entry into the cell and also activates a protein kinase-dependent mechanism for sodium pump stimulation. The protein kinase-dependent mechanism does not appear to be triggered by an increased rate of sodium entry since staurosporine did not prevent the stimulation of ouabain-sensitive potassium (86Rb) uptake elicited by an increase in sodium permeability caused by amphotericin B.

The role of the spleen, especially regarding changes in both thromboxane A2 and the remnant liver dysfunction after extensive hepatectomy

The plasma levels of thromboxane B2 (TxB2) and 6-keto-prostaglandin F1alpha (6-KF) in the peripheral and portal blood increase after an extensive hepatectomy, and even more so in cases with complications. In this cell biological study, we estimated the prostanoids in the portal system to clarify which organ produces them, while also evaluating the effect of a splenectomy in conjunction with an extensive hepatectomy. Our results showed that the level of TxB2 in the splenic vein was significantly higher than that in the mesenteric vein. Furthermore, the TxA2 produced by splenic macrophages after an extensive hepatectomy was significantly more than after a sham operation. We also observed the hepatocyte damage to be less in the group that underwent an 84% hepatectomy and splenectomy than in the group that underwent the same hepatectomy without a splenectomy. It therefore appears important both to suppress the splenic macrophages from producing TxA2 and to prevent remnant hepatic dysfunction after an extensive hepatectomy.

Calcium vs. iron-mediated processes in hydrogen peroxide toxicity to L929 cells: effects of glucose

H2O2 toxicity was studied in L929 cells in the presence and absence of glucose. The data obtained in the absence of glucose suggest a Ca2+-dependent mechanism of cell injury. No evidence was found for any involvement of iron in the process. In particular, cell injury was unaffected by the intracellular iron chelators 2,2'-dipyridyl and deferoxamine or by the hydroxyl radical scavengers DMSO and DMPO. On the other hand, the intracellular Ca2+ chelator BAPTA/AM provided significant protection. The cytosolic Ca2+ level rapidly and consistently increased after H2O2 addition, prior to visible bleb formation and loss of cell viability. Additionally, GSH not only prevented cell death but also significantly decreased cytosolic calcium accumulation. In the presence of glucose, however, Ca2+ does not seem to play any role in H2O2 toxicity. Cell death is now mainly mediated by iron: the iron chelators and hydroxyl radical scavengers prevented cell injury, the increase in cytosolic Ca2+ was significantly less pronounced, and BAPTA/AM did not exert any protection under these conditions. Hence, the metabolic state of the L929 cells, as given by the availability of glucose, decisively determines the biochemical mechanism of H2O2 cell injury.

Microvilli elongate in response to hydrogen peroxide and to perturbations of intracellular calcium

Using scanning electron microscopy and fluorescence microscopy, we have found that apical microvilli of diverse cell types, including nonepithelial cells, elongate in culture in response to the oxidative stress of hydrogen peroxide. The microvilli induced in culture on retinal pigment epithelial cells display a 30-nm axial periodicity similar to that described for stable microvilli of intestinal brush border. Microvilli can also be induced to elongate by chelating intracellular Ca2+ and by the Ca(2+)-uptake inhibitor thapsigargin. Thus a response of microvillar protrusion occurs widely and may be related to depletion of intracellular calcium stores.

Contrasting effects of hypochlorous acid and hydrogen peroxide on endothelial permeability: prevention with cAMP drugs

Activated polymorphonuclear leukocytes generate a cascade of reduced oxygen metabolites. In addition to their antimicrobial role, hydrogen peroxide (H2O2) and hypochlorous acid (HOCl) function as inflammatory mediators and increase the protein permeability of the vascular endothelium. The objectives of the present study were to compare the effects of H2O2 and HOCl with respect to relative potencies and the time course and magnitude of changes in cell shape and permeability of endothelial cell monolayers derived from bovine pulmonary artery, to determine if HOCl produced by conversion of H2O2 with myeloperoxidase and Cl- produces comparable results as the direct administration of HOCl, and to show that adenosine 3',5'-cyclic monophosphate (cAMP)-enhancing agents can prevent the increased endothelial permeability induced by HOCl and H2O2. HOCl given directly or produced by myeloperoxidase, H2O2, and Cl- caused faster and greater changes in cell shape (cell retraction), electrical resistance, and protein permeability (125I-labeled albumin clearance) of endothelial cell monolayers than induced by H2O2. HOCl (10 to 100 microM) induced these changes within 1 to 3 min, whereas H2O2 (50 to 400 microM) required approximately 30 min. 8-Bromo-cAMP prevented the increased endothelial protein permeability induced by HOCl or H2O2, but isoproterenol only prevented the H2O2 response. Thus, HOCl at a much lower concentration caused a faster and greater increase in endothelial permeability in vitro than H2O2, and an increased intracellular level of cAMP prevented the increased permeability induced by either oxidant.

Ionic mechanism of the effects of hydrogen peroxide in rat ventricular myocytes

1. Whole-cell and amphotericin-perforated patch-clamp techniques have been used to study the effects of hydrogen peroxide (H2O2) on action potentials and underlying ionic currents in single myocytes from the ventricles of adult rat hearts. 2. The results obtained differed markedly depending on the recording method utilized. Conventional whole-cell recordings, in which the myoplasm is dialysed with the contents of the pipette, failed to show any significant effects of H2O2 on the action potential or cell shortening. In contrast, when action potentials were recorded with the amphotericin-perforated patch method, H2O2 (50-200 microM) produced a marked prolongation of the action potential and an increase in cell shortening. 3. Voltage-clamp recordings with the amphotericin-perforated patch method showed that H2O2 caused no significant changes in either the Ca(2+)-independent transient outward K+ current (Ito) or the inwardly rectifying K+ current (IK1). 4. Application of tetrodotoxin (TTX; 8 x 10(-6) M), a Na+ channel blocker, largely inhibited the effects of H2O2 on the action potential. Moreover, anthopleurin A (4 x 10 (-7) M), which augments Na+ current (INa) by slowing its inactivation, mimicked the effects of H2O2 on the action potential of ventricular myocytes. These effects on INa were also blocked almost completely by TTX. 5. The hypothesis that H2O2 can augment INa by slowing its kinetics of inactivation was tested directly using ensemble recordings from cell-attached macropatches. These results demonstrated a significant enhancement of late opening events when H2O2 (200 microM) was included in the recording pipette. A corresponding slowing of inactivation of the ensemble INa was observed. 6. The possibility that protein kinase C (PKC) is an intracellular second messenger for the observed effects of H2O2 was examined using the blocker bisindolylmaelimide (BIS; 10(-7) M). Bath application of BIS prior to H2O2 exposure significantly delayed and also attenuated the development of the action potential prolongation. 7. These results demonstrate marked electrophysiological effects of H2O2 in rat ventricle. The dependence of these effects on recording methods suggests involvement of an intracellular second messenger, and the results with the PKC inhibitor, BIS, support this possibility. The most prominent effect of H2O2 on the ionic currents which underlie the action potential is a slowing of inactivation of the TTX-sensitive INa. Recent molecular studies have demonstrated a PKC phosphorylation site on the rat cardiac Na+ channel isoform and have also shown that PKC activation can slow inactivation of INa.

Flow cytometric analysis of the H2O2-induced increase in intracellular Ca2+ concentration of rat thymocytes

The effect of hydrogen peroxide (H2O2) on the intracellular Ca2+ concentration ([Ca2+]i) of rat thymocytes was examined by a flow cytometer and two fluorescent dyes, fluo-3-AM and ethidium bromide, a dye impermeant to intact membranes, to characterize the H2O2-induced increase in [Ca2+]i. H2O2 at concentrations greater than 30 microM dose-dependently increased the [Ca2+]i of thymocytes which were not stained with ethidium. Removal of external Ca2+ greatly reduced the degree of H2O2-induced increase in [Ca2+]i. However, H2O2 still increased the [Ca2+]i under the external Ca(2+)-free condition. Diethylmaleate, which is known to produce a chemical depletion of cellular nonprotein thiol, significantly increased the [Ca2+]i. Dithiothreitol, which is used to protect cellular nonprotein thiol, slightly decreased the [Ca2+]i, but greatly reduced the H2O2-induced increase in [Ca2+]i. Therefore, it is considered that H2O2 may increase the [Ca2+]i through a mechanism related to the effects of H2O2 on the cellular nonprotein thiol.

The phosphorylation state of MAP-kinases modulates the cytotoxic response of smooth muscle cells to hydrogen peroxide

Micromolar concentrations of hydrogen peroxide induced the phosphorylation of mitogen-activated protein (MAP) kinases and a lethal response in growth-arrested smooth muscle cells (A7r5). The H202-induced phosphorylation of MAP-kinases was markedly lower in the presence of protein tyrosine kinase (PTK) inhibitors or in protein kinase C (PKC) down-regulated cells. Similarly, the toxicity of H202 was diminished by concomitant addition of either PKC or PTK inhibitors and was also lower in PKC down-regulated cells. These results are consistent with the possibility that phosphorylation of MAP-kinases is a critical event in the toxic response of cultured smooth muscle cells to H202.

Homocysteine mediated endothelial cell toxicity and its amelioration

In response to homocysteine induced toxicity in human umbilical vein endothelial cells, minimal changes in the concentration of cellular protein thiols but substantial changes in the concentration of intracellular soluble thiols were observed. The latter correlated closely with changes in cellular glutathione levels. No correlation existed between cellular glutathione levels and cell viability, whereas a close correlation between NAD+ levels and cell viability was demonstrated. Large decreases in cellular NAD+ occurred in response to homocysteine induced toxicity which were accompanied by the production of single stranded DNA. 3-Aminobenzamide, an inhibitor of poly (ADP-ribose) polymerase preserved cell viability and cellular NAD+ levels. Evidence that DNA synthesis was also compromised was revealed by the decreased capacity of homocysteine treated cells to incorporate deoxyuridine. Radical scavengers were also effective in preventing homocysteine induced toxicity. It is likely that the major threat to cells derives from radicals generated intracellularly. Eicosanoid metabolism and the xanthine oxidase system have been identified as two potential sources of radicals.

Cooperation of tyrosine kinases p72syk and p53/56lyn regulates calcium mobilization in chicken B cell oxidant stress signaling

A chicken B cell line DT40 and its syk-negative or lyn-negative mutants were used to investigate the roles of protein-tyrosine kinases in oxidant stress signaling. The data presented here for wild-type cells demonstrate that hydrogen peroxide stimulates p53/56lyn-dependent tyrosine phosphorylation and activation of p72syk, and induces a rapid and prolonged elevation of intracellular calcium, which consists of calcium release from intracellular stores and influx from the extracellular space. Hydrogen-peroxide-triggered calcium mobilization was impaired in both syk-negative and lyn-negative cells, which was mainly due to the loss of calcium release from intracellular stores. Further studies indicated that inositol trisphosphate production was also abolished in both syk-negative and lyn-negative cells, which is consistent with the loss of calcium release. Taken together, these observations suggest that the defect of p72syk or p53/56lyn was responsible for the abnormality of calcium mobilization in both lyn-negative and syk-negative cells, and that both p72syk and p53/56lyn might regulate calcium mobilization through the phosphatidylinositol pathway in B cell oxidant stress signaling.

Role of intracellular signalling pathways in hydrogen peroxide-induced injury to rat glomerular mesangial cells

1. Brief exposure of cultured rat glomerular mesangial cells (GMC) to H2O2 in nominally bicarbonate-free solution induced a rapid dose dependent, dantrolene-inhibitable increase in intracellular free Ca2+ from 65 +/- 6 to 203 +/- 14 nmol/L and a prolonged release of [14C]-arachidonic acid [14C]-AA which preceded the onset of cell membrane damage assessed by trypan-blue uptake. 2. Ca2+ responses were potentiated in HCO3-/CO2 containing buffers and reached values of 1145 +/- 100 nmol/L at 1 mmol/L H2O2. In HCO3-/CO2 solutions, but not HEPES buffer, H2O2-induced Ca2+ increases were markedly attenuated by verapamil (100 mumol/L) or removal of extracellular calcium. 3. Enhanced release of [14C]-AA was partially attenuated by inhibitors of key intracellular signalling mechanisms including the phospholipase-A2 (PLA2) inhibitor mepacrine (100 mumol/L), the NADPH oxidase inhibitor diphenyliodonium (10 mumol/L), the mitochondrial calcium-cycling inhibitor ruthenium red (10 mumol/L) and the iron chelator dipyridyl (100 mumol/L). Release was unaffected by protein kinase C inhibition with H7 (100 mumol/L), inositol triphosphate antagonism with neomycin (1 mmol/L) or overnight treatment with the G-protein antagonist pertussis toxin (5 micrograms/mL). 4. Several structurally diverse lipoxygenase inhibitors, including esculetin, baicalein and phenidone, over the dose range 1-100 mumol/L, also prevented [14C]-AA release and markedly protected against cell membrane damage. No drug directly scavenged H2O2 assessed by UV absorption. 5. These results indicate that H2O2 activates in GMC a complex series of interrelated pathological mechanisms which in turn contribute to a prolongation of oxidative damage beyond the time of the initial exposure. These include an increase in intracellular calcium which, depending upon conditions, appears to be mediated by release from intracellular stores as well as Ca2+ entry from the extracellular space. In turn there is a sustained release of arachidonic acid, which may partly depend on prolonged activation of PLA2 but not phospholipase C. 6. Release of [14C]-AA could be attenuated by inhibitors of NADPH oxidase, mitochondrial calcium-cycling, iron chelators and a structurally diverse range of lipoxygenase inhibitors in association with protection from H2O2-mediated cell membrane damage.

Reduced glutathione esters--antidotes to toxicity. Cytotoxicity induced by hydrogen peroxide, 1-chloro-2,4-dinitrobenzene, and menadione in murine P388D1 macrophages in vitro

Repletion of depleted cellular reduced glutathione (GSH) levels in oxidative stress and exposure to arylating agents is a strategy for the development of antidotes to chemical toxicity. The effect of GSH, reduced glutathione ethyl monoester (GSHEt), and reduced glutathione ethyl diester (GSHEt2) on the cytotoxicity of hydrogen peroxide, 1-chloro-2,4-dinitrobenzene (CDNB), and menadione to P388D1 macrophages in vitro was investigated. The median toxic concentration TC50 values of the toxicants were hydrogen peroxide 24 +/- 2 mM (N = 19), CDNB 63 +/- 6 microM (N = 18), and menadione 30 +/- 4 microM (N = 22). Reduced glutathione, GSHEt, and GSHEt2 were poor antidotes to hydrogen peroxide toxicity. Indeed, the observed antidote effects were attributed to the nonenzymatic reaction of the GSH derivatives with hydrogen peroxide in the extracellular medium. Reduced glutathione ethyl diester was a more potent antidote of CDNB- and menadione-mediated toxicity than GSHEt and GSH. For cell incubations with the approximate median toxic concentration TC50 values of hydrogen peroxide, CDNB, and menadione, the respective median effective antidote concentration EC50 values were GSHEt 23.8 +/- 4.1 mM (N = 9), 3.6 +/- 0.6 mM (N = 11), and 226 +/- 93 microM (N = 12); and GSHEt2 20.4 +/- 1.9 mM (N = 6), 603 +/- 2 microM (N = 9), and 7.6 +/- 2.3 microM (N = 12). Reduced glutathione ethyl diester was a potent antidote to CDNB- and menadione-induced toxicities but not to hydrogen peroxide-induced toxicity under acute intoxication conditions.

Inhibition of oxidative insult in cultured cells by a novel 6-chromanol-containing antioxidant

N18-RE-105 neuronal hybridoma cells were used in a cell culture system to evaluate the protective effects of a novel 6-chromanol-containing antioxidant, U78517F. First, the incorporation of the compound into the cells was evaluated, using a serum albumin carrier. Then the cells were exposed to peroxide-generating compounds, and the cell injury was estimated from the loss of alpha-aminoisobutyric acid (AIB) transport. We found that U78517F only protected the cells significantly when the degree of oxidative insult was below a certain limit; the measurable protection of cells by U78517F against either cumene hydroperoxide or H2O2 was limited to a narrow range of concentrations of the reactive oxygen species generator. Additionally, the protection provided by U78517F was largely localized to the cell membrane and did not extend to protection of mitochondrial function. The action of U78517 was fully consistent with a direct radical scavenging in the cells. The results indicate that the following factors must be taken into account for evaluation of antioxidants in cell culture: (a) the delivery of a compound to cells, especially when the compound is lipophilic; (b) the nature and extent of the oxidative insult used to evaluate protection; and (c) the location of the protective agent in the cells.

Role of [Ca2+]i in lethal oxidative injury in rat cultured inner medullary collecting duct cells

Reactive oxygen metabolites have been implicated in the pathogenesis of toxic, ischaemic and immunologically mediated renal injury. An increase in the cytosolic free Ca2+ concentration ([Ca2+]i) has been proposed as a mechanism of oxidative stress-induced cell injury. We used a fluorescence spectrometer and a fluorescence probe to measure the [Ca2+]i and viability of rat primary cultured inner medullary collecting duct (IMCD) cells during oxidative stress induced by 5 mM tert-butyl hydroperoxide (TBHP). Initially, this oxidative stress evoked a small increase in [Ca2+]i which was followed by a slower sustained increase from the resting level of 170.8 +/- 38.8 nM to 1490.5 +/- 301.7 nM after 60 min, and this preceded the loss of plasma membrane integrity, measured by the propidium iodide fluorescence method. The elimination of extracellular Ca2+ from the culture medium prevented the TBHP-induced [Ca2+]i increase and improved cell viability. Restoration of extracellular Ca2+ resulted in an immediate and large increase in [Ca2+]i and extensive cell death. Verapamil, a Ca2+ channel blocker, inhibited the [Ca2+]i increase and afforded significant protection against cellular injury following exposure to TBHP-induced oxidative stress. Extracellular acidosis also prevented the increase in [Ca2+]i and cell death caused by this oxidative stress. These results are consistent with the hypothesis that oxidative stress-induced IMCD cellular injury may be the result of increased [Ca2+]i caused, in part, by activation of voltage-dependent Ca2+ channels.

The effect of active oxygen generated by xanthine/xanthine oxidase on genes and signal transduction in mouse epidermal JB6 cells

To gain insight into the gene regulation and signal transduction effects of active oxygen in tumour promotion and progression, we studied the effect of active oxygen generated extracellularly by xanthine/xanthine oxidase (X/XO) in promotion-insensitive (P-), promotion-sensitive (P+) and transformed (Tx) mouse epidermal JB6 cells. Active oxygen inhibited growth, particularly of P- cells and increased poly ADPR transferase activity and PKC activity more significantly in P- cells. No phenotypic differences in the distribution pattern of PKC isotypes alpha, beta and gamma were seen in JB6 cells. PKC alpha was expressed abundantly, whereas beta and gamma were not detected. Basal levels of the antioxidant enzymes catalase and CuZn. Superoxide dismutase were higher in P+ and Tx cells. X/XO resulted in an initial decrease in the activity of these enzymes, followed by recovery or transient induction in Tx and P+ cells. X/XO induced c-myc and c-fos expression in JB6 cells, with c-fos induction being more pronounced in P- cells, whereas a biphasic increase in c-jun was seen in P+ cells. These early genes may play a role in proliferation whereas post-translational poly ADP-ribosylation and, perhaps, phosphorylation suggest a genetic-epigenetic mechanism in oxidant tumour promotion and progression.

Pulmonary microsomes contain a Ca(2+)-transport system sensitive to oxidative stress

A variety of events, including inhalation of atmospheric chemicals, trauma, and ischemia-reperfusion, may cause generation of reactive oxygen species in the lung and result in airways constriction. The specific metabolic mechanisms that translate oxygen radical production into airways constriction are yet to be identified. In the lung, calcium homeostasis is central to release of bronchoactive and vasoactive chemical mediators and to regulation of smooth muscle cell contractility, i.e., airway constriction. In the present work, we characterized Ca(2+)-transport in the microsomal fraction of mouse lungs, and determined how reactive oxygen species, generated by Fe2+/ascorbate and H2O2/hemoglobin, affected Ca2+ transport. The microsomal fraction of pulmonary tissue accumulated 90 +/- 5 nmol Ca2+/mg protein by an ATP-dependent process in the presence of 15 mM oxalate, and 16 +/- 2 nmol Ca2+ in its absence. In the presence of oxalate, the rate of Ca2+ uptake was 50 +/- 5 nmol Ca2+/min per mg protein at pCa 5.9 (37 degrees C). The Ca(2+)-ATPase activity was 50-60 nmol Pi/min per mg protein (pCa 5.9, 37 degrees C) in the presence of alamethicin. Inhibitors of mitochondrial H(+)-ATPase had no effect on the Ca2+ transport. Half-maximal activation of Ca2+ transport was produced by 0.4-0.5 microM Ca2+. Endoplasmic reticulum Ca(2+)-pump (SERC-ATPase) was found to be predominantly responsible for the Ca(2+)-accumulating capacity of the pulmonary microsomes. Incubation of the microsomes in the presence of either Fe2+/ascorbate or H2O2/hemoglobin resulted in a time-dependent accumulation of peroxidation products (TBARS) and in inhibition of the Ca2+ transport. The inhibitory effect of Fe2+/ascorbate on Ca2+ transport strictly correlated with the inhibition of the Ca(2+)-ATPase activity. These results are the first to indicate a highly active microsomal Ca2+ transport system in murine lungs which is sensitive to endogenous oxidation products. The importance of this system to pulmonary disorders exacerbated by oxidative chemicals remains to be studied.

The effect of histamine on the oxidative burst of HL60 cells before and after exposure to reactive oxygen species

During an inflammation neutrophils are stimulated to produce reactive oxygen species (ROS). These ROS induce the release of histamine from mast cells, which are also present at the inflammation site. In this study dibutyryl cAMP differentiated HL60 cells are used as a model for human neutrophils. The effect of histamine on formyl-methionyl-leucyl-phenylalanine (fmlp) stimulated cells is examined. Except for histamine also an accumulation of ROS takes place at the inflammation site and we investigated if ROS can influence the response of the stimulated HL60 cells. It is found that 10(-3) M histamine can inhibit the fmlp induced superoxide anion radical production. This occurs partly via an H2 receptor because H2 antagonists like famotidine, mifentidine and ranitidine could partially antagonize this effect of histamine. When HL60 cells are exposed to hydrogen peroxide or hypochlorous acid (20 min), an increased fmlp response is found while the inhibiting effect of histamine remains unchanged.

Measurement of striatal H2O2 by microdialysis following global forebrain ischemia and reperfusion in the rat: correlation with the cytotoxic potential of H2O2 in vitro

Toxic reactive oxygen species have been implicated as important mediators of tissue injury after reperfusion of ischemic organs. When rats are subject to 30 min global forebrain ischemia, 24 h following this insult, there is substantial loss of medium-sized neurones as revealed by histological sectioning of the striatal region of the forebrain. The goal of this study was to utilize microdialysis to directly measure one of the more stable intermediates of reduced molecular oxygen, H2O2 in the rat striatum following 4-vessel occlusion and reperfusion, and to correlate these levels with H2O2 toxicity to neurones grown in culture. A significant rise in striatal H2O2 levels was observed for about 1 h during reperfusion, amounting to an increase of approximately 100 microM at the peak. In control experiments where the dialysis probe was embedded in cortical regions surrounding the striatum (where there is no neuronal loss due to the ischemic episode), there was no measurable increase in tissue H2O2 levels. H2O2 has been previously shown to be neurotoxic to PC12 cells as well as rat primary hippocampal neurones at comparable concentrations striatal neurones experience during reperfusion. We demonstrate that H2O2 is also neurotoxic to the human cortical neuronal cell line, HCN-1A. These experiments establish an important link between oxidant generation and neuronal loss in this tissue following global forebrain ischemia.

Modulation of the alveolar macrophage respiratory burst by hydroperoxides

Exposure of alveolar macrophages to hydroperoxides (ROOH) inhibits subsequent stimulation of O2.- production (the respiratory burst). Previous studies (under nonoxidant stress conditions) have shown that elevation of intracellular free calcium ([Ca2+]i) participates in both initiation and termination of O2.- production. In this investigation, the effects of sublethal ROOH exposure on [Ca2+]i and the respiratory burst of rat alveolar macrophages were compared. Exposure to a sublethal range of H2O2 or tert-butylhydroperoxide (10-100 pmol/10(6) cells; initially 10-100 microM under the experimental conditions) for 15 min resulted in dose-dependent effects on the respiratory burst stimulated by various agents, ADP, ATP, zymosan-activated serum, and phorbol myristate acetate. Low concentrations of the ROOH (10 or 25 pmol/10(6) cells) were found to enhance stimulation, whereas exposure to 75 or 100 pmol/10(6) cells resulted in significant inhibition for all of the stimuli. All concentrations of ROOH caused a rapid elevation in [Ca2+]i. For those concentrations of ROOH that produced enhancement of subsequent stimulation of the respiratory burst, [Ca2+]i returned to near baseline before the end of the 15-min preincubation. The temporal- and concentration-dependent effects of ROOH on [Ca2+]i correlate with subsequent enhancement or inhibition of stimulated O2.- production. Similarities between the ROOH-induced changes in [Ca2+]i and the effect of [Ca2+]i changes in physiological regulation of the respiratory burst suggest a potential relationship.

Activation of murine macrophages by hydrogen peroxide

Hydrogen peroxide at concentrations from 0.1 to 20 microM enhances phagocytosis and oxidative burst of murine peritoneal macrophages. The activation of these macrophage functions is paralleled by prolonged hyperpolarization and a transient increase in cytoplasmic free calcium concentration. All the effects are dose- and time-dependent. The results obtained for H2O2 are compared with those for a natural activator, peptide N-formyl-methionyl-leucyl-phenylalanine. The data demonstrate the ability of small doses of hydrogen peroxide to stimulate macrophages through the intracellular mechanisms of ion transduction.

Impairment of integrin-mediated cell-matrix adhesion in oxidant-stressed PC12 cells

Oxidants are believed to play an important and complex role in neuronal injury and death in the aging process and various neurode generative diseases. We studied the effect of oxidative stress on integrin-mediated cell-extracellular matrix (ECM) interactions using the PC12 neuronal cell line. In assays in which attachment was measured between 30 and 90 min, addition of hydrogen peroxide (H2O2) to the attachment medium resulted in a dose-dependent inhibition of initial cell attachment to collagen. Addition of H2O2 also caused previously attached cells to detach from collagen. The inhibition by H2O2 was specific for integrin-mediated adhesion, since attachment to substrata coated with non-ECM molecules was much less affected. Exposure of cells to H2O2 resulted in a rapid and profound reduction of intracellular ATP, accompanied by only a slight increase in intracellular free Ca2+ concentration ([Ca2+]i). Treatment of cells with the microfilament-disrupting agent, cytochalasin B, like that with H2O2, inhibited cell adhesion to collagen. We propose that integrin-mediated cell adhesion, which requires interactions between cytoplasmic portions of integrin subunits and cytoskeletal microfilaments, is impaired by oxidative stress as a result of the depletion of intracellular ATP and that such depletion is an early event in the process of oxidant-induced neuronal injury.

Hydrogen peroxide activates agonist-sensitive Ca(2+)-flux pathways in canine venous endothelial cells

The effect of the biological oxidant H2O2 on purinergic-receptor-stimulated Ca2+ signalling was determined in canine venous endothelial cells. H2O2 increased cytosolic free [Ca2+] ([Ca2+]i), the rate of rise of which was dose-dependently related to H2O2 concentration. The response of [Ca2+]i to H2O2 resulted in part from release of Ca2+ from internal stores. The H2O2-sensitive intracellular Ca2+ pool was characterized in cells suspended in Ca(2+)-free/EGTA buffer and stimulated in sequence with H2O2 and ionomycin or ATP. Under this condition, the rank order of apparent compartment size sensitive to each compound was ionomycin > H2O2 > ATP. Stimulation of cells with H2O2 eliminated any response of [Ca2+]i to subsequent addition of ATP. To test more directly whether H2O2 accesses the inositol trisphosphate-sensitive Ca2+ store, cells were pretreated with thapsigargin, a selective inhibitor of that store's Ca2+ pump. Release of Ca2+ from internal Ca2+ stores by H2O2 declined as the interval after thapsigargin addition increased, a finding that supports the contention that H2O2 accesses the inositol trisphosphate-sensitive Ca2+ store. H2O2-stimulated Ca2+ influx across the cell membrane was sensitive to Ni2+, La3+, and 1-(beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl)-1H-imidazole HCl (SKF-96365), a selective inhibitor of the agonist-stimulated Ca(2+)-influx pathway. Ca2+ entry triggered by H2O2 appears to occur via the agonist-sensitive Ca2+ influx pathway. Together, these results suggest that H2O2, which is normally secreted by activated neutrophils and monocytes, may act as an intercellular messenger and stimulate Ca2+ signalling in target endothelial cells.

Evidence suggesting that iron and calcium are interrelated in oxidant-induced DNA damage

The effect of iron chelators and agents that buffer cytosolic-free calcium ([Ca2+]i) on hydrogen peroxide-induced DNA strand breaks in LLC-PK1 cells has not been previously examined. In addition, the interrelationship between iron and calcium in the pathogenesis of DNA damage has not been studied in any model of tissue injury. Exposure of LLC-PK1 cells to 1 mM hydrogen peroxide resulted in marked DNA damage, as measured by the alkaline unwinding assay (residual intact double stranded DNA at 10 min, control: 88 +/- 1%; hydrogen peroxide-treated cells: 17 +/- 3%, N = 8). The iron chelators, 1,10-phenanthroline and deferoxamine, and agents which buffer [Ca2+]i, BAPTA and quin-2, provided highly significant protection against hydrogen peroxide-induced DNA strand breaks. We then examined the effect of iron chelators on hydrogen peroxide-induced rise in [Ca2+]i in LLC-PK1 cells. Both 1,10-phenanthroline and deferoxamine prevented the marked and sustained rise in [Ca2+]i induced by exposure of LLC-PK1 cells to 1 mM hydrogen peroxide ([Ca2+]i at 15 min, control 100 +/- 3 nM; hydrogen peroxide 195 +/- 14 nM; 1,10-phenanthroline + hydrogen peroxide 100 +/- 4 nM; deferoxamine + hydrogen peroxide 106 +/- 4 nM; N = 4). We excluded the possibility that the iron chelators were directly chelating calcium by performing experiments using a cell free system. We also confirmed that BAPTA and quin-2, in concentrations used in our study, chelate calcium but not iron or copper.(ABSTRACT TRUNCATED AT 250 WORDS)