Hydrogen peroxide increases the intracellular calcium activity in rat mesangial cells in primary culture

GPR4 Knockout Improves the Neurotoxin-Induced, Caspase-Dependent Mitochondrial Apoptosis of the Dopaminergic Neuronal Cell

In Parkinson’s disease, mitochondrial oxidative stress-mediated apoptosis is a major cause of dopaminergic neuronal loss in the substantia nigra (SN). G protein-coupled receptor 4 (GPR4), previously recognised as an orphan G protein coupled-receptor (GPCR), has recently been claimed as a member of the group of proton-activated GPCRs. Its activity in neuronal apoptosis, however, remains undefined. In this study, we investigated the role of GPR4 in the 1-methyl-4-phenylpyridinium ion (MPP⁺) and hydrogen peroxide (H₂O₂)-treated apoptotic cell death of stably GPR4-overexpressing and stably GPR4-knockout human neuroblastoma SH-SY5Y cells. In GPR4-OE cells, MPP⁺ and H₂O₂ were found to significantly increase the expression levels of both mRNA and proteins of the pro-apoptotic Bcl-2-associated X protein (Bax) genes, while they decreased the anti-apoptotic B-cell lymphoma 2 (Bcl-2) genes. In addition, MPP⁺ treatment activated Caspase-3, leading to the cleavage of poly (ADP-ribose) polymerase (PARP) and decreasing the mitochondrial membrane potential (ΔΨm) in GPR4-OE cells. In contrast, H₂O₂ treatment significantly increased the intracellular calcium ions (Ca²⁺) and reactive oxygen species (ROS) in GPR4-OE cells. Further, chemical inhibition by NE52-QQ57, a selective antagonist of GPR4, and knockout of GPR4 by clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 decreased the Bax/Bcl-2 ratio and ROS generation, and stabilised the ΔΨm, thus protecting the SH-SY5Y cells from MPP⁺- or H₂O₂-induced apoptotic cell death. Moreover, the knockout of GPR4 decreased the proteolytic degradation of phosphatidylinositol biphosphate (PIP₂) and subsequent release of the endoplasmic reticulum (ER)-stored Ca²⁺ in the cytosol. Our results suggest that the pharmacological inhibition or genetic deletion of GPR4 improves the neurotoxin-induced caspase-dependent mitochondrial apoptotic pathway, possibly through the modulation of PIP₂ degradation-mediated calcium signalling. Therefore, GPR4 presents a potential therapeutic target for neurodegenerative disorders such as Parkinson’s disease.

Simultaneous fluorescence visualization of mitochondrial hydrogen peroxide and zinc ions in live cells and in vivo

We have developed two new fluorescent probes termedM-H2O2andM-Znfor simultaneous imaging of hydrogen peroxide and zinc ions in mitochondria.

Hydrogen peroxide stimulation of CFTR reveals an Epac-mediated, soluble AC-dependent cAMP amplification pathway common to GPCR signalling

BACKGROUND AND PURPOSE

H2 O2 is widely understood to regulate intracellular signalling. In airway epithelia, H2 O2 stimulates anion secretion primarily by activating an autocrine PGE2 signalling pathway via EP4 and EP1 receptors to initiate cytic fibrosis transmembrane regulator (CFTR)-mediated Cl(-) secretion. This study investigated signalling downstream of the receptors activated by H2 O2 .

EXPERIMENTAL APPROACH

Anion secretion by differentiated bronchial epithelial cells was measured in Ussing chambers during stimulation with H2 O2 , an EP4 receptor agonist or β2 -adrenoceptor agonist in the presence and absence of inhibitors of ACs and downstream effectors. Intracellular calcium ([Ca(2+) ]I ) changes were followed by microscopy using fura-2-loaded cells and PKA activation followed by FRET microscopy.

KEY RESULTS

Transmembrane adenylyl cyclase (tmAC) and soluble AC (sAC) were both necessary for H2 O2 and EP4 receptor-mediated CFTR activation in bronchial epithelia. H2 O2 and EP4 receptor agonist stimulated tmAC to increase exchange protein activated by cAMP (Epac) activity that drives PLC activation to raise [Ca(2+) ]i via Ca(2+) store release (and not entry). Increased [Ca(2+) ]i led to sAC activation and further increases in CFTR activity. Stimulation of sAC did not depend on changes in [HCO3 (-) ]. Ca(2+) -activated apical KCa 1.1 channels and cAMP-activated basolateral KV 7.1 channels contributed to H2 O2 -stimulated anion currents. A similar Epac-mediated pathway was seen following β2 -adrenoceptor or forskolin stimulation.

CONCLUSIONS AND IMPLICATIONS

H2 O2 initiated a complex signalling cascade that used direct stimulation of tmACs by Gαs followed by Epac-mediated Ca(2+) crosstalk to activate sAC. The Epac-mediated Ca(2+) signal constituted a positive feedback loop that amplified CFTR anion secretion following stimulation of tmAC by a variety of stimuli.

Differential expression of sPLA2 following spinal cord injury and a functional role for sPLA2-IIA in mediating oligodendrocyte death

After the initial mechanical insult of spinal cord injury (SCI), secondary mediators propagate a massive loss of oligodendrocytes. We previously showed that following SCI both the total phospholipase activity and cytosolic PLA(2)-IV alpha protein expression increased. However, the expression of secreted isoforms of PLA(2) (sPLA(2)) and their possible roles in oligodendrocyte death following SCI remained unclear. Here we report that mRNAs extracted 15 min, 4 h, 1 day, or 1 month after cervical SCI show marked upregulation of sPLA(2)-IIA and IIE at 4 h after injury. In contrast, SCI induced down regulation of sPLA(2)-X, and no change in sPLA(2)-IB, IIC, V, and XIIA expression. At the lesion site, sPLA(2)-IIA and IIE expression were localized to oligodendrocytes. Recombinant human sPLA(2)-IIA (0.01, 0.1, or 2 microM) induced a dose-dependent cytotoxicity in differentiated adult oligodendrocyte precursor cells but not primary astrocytes or Schwann cells in vitro. Most importantly, pretreatment with S3319, a sPLA(2)-IIA inhibitor, before a 30 min H(2)O(2) injury (1 or 10 mM) significantly reduced oligodendrocyte cell death at 48 h. Similarly, pretreatment with S3319 before injury with IL-1 beta and TNFalpha prevented cell death and loss of oligodendrocyte processes at 72 h. Collectively, these findings suggest that sPLA(2)-IIA and IIE are increased following SCI, that increased sPLA(2)-IIA can be cytotoxic to oligodendrocytes, and that in vitro blockade of sPLA(2) can create sparing of oligodendrocytes in two distinct injury models. Therefore, sPLA(2)-IIA may be an important mediator of oligodendrocyte death and a novel target for therapeutic intervention following SCI.

Hydrogen peroxide mobilizes Ca2+ through two distinct mechanisms in rat hepatocytes

AIM

Hydrogen peroxide (H2O2) is produced during liver transplantation. Ischemia/reperfusion induces oxidation and causes intracellular Ca2+ overload, which harms liver cells. Our goal was to determine the precise mechanisms of these processes.

METHODS

Hepatocytes were extracted from rats. Intracellular Ca2+ concentrations ([Ca2+](i)), inner mitochondrial membrane potentials and NAD(P)H levels were measured using fluorescence imaging. Phospholipase C (PLC) activity was detected using exogenous PIP2. ATP concentrations were measured using the luciferin-luciferase method. Patch-clamp recordings were performed to evaluate membrane currents.

RESULTS

H2O2 increased intracellular Ca2+ concentrations ([Ca2+](i)) across two kinetic phases. A low concentration (400 micromol/L) of H2O2 induced a sustained elevation of [Ca2+](i) that was reversed by removing extracellular Ca2+. H2O2 increased membrane currents consistent with intracellular ATP concentrations. The non-selective ATP-sensitive cation channel blocker amiloride inhibited H2O2-induced membrane current increases and [Ca2+](i) elevation. A high concentration (1 mmol/L)of H2O2 induced an additional transient elevation of [Ca2+](i), which was abolished by the specific PLC blocker U73122 but was not eliminated by removal of extracellular Ca2+. PLC activity was increased by 1 mmol/L H2O2 but not by 400 micromol/L H2O2.

CONCLUSIONS

H2O2 mobilizes Ca2+ through two distinct mechanisms. In one, 400 micromol/L H2O2-induced sustained [Ca2+](i) elevation is mediated via a Ca2+ influx mechanism, under which H2O2 impairs mitochondrial function via oxidative stress,reduces intracellular ATP production, and in turn opens ATP-sensitive, non-specific cation channels, leading to Ca2+ influx.In contrast, 1 mmol/L H2O2-induced transient elevation of [Ca2+](i) is mediated via activation of the PLC signaling pathway and subsequently, by mobilization of Ca2+ from intracellular Ca2+ stores.

Mechanism underlying H2O2-induced inhibition of acetylcholine-induced contraction in rabbit tracheal smooth muscle

The mechanism underlying the inhibition by H2O2 of acetylcholine-induced contraction was investigated in epithelium-denuded strips of rabbit trachea. Acetylcholine (10 microM) generated a phasic, followed by a tonic increase in both the intracellular Ca2+ concentration ([Ca2+]i) and force. Although the acetylcholine-induced tonic contraction was around 9 times the high K+ (80 mM)-induced one, the two stimulants induced similar [Ca2+]i increases (around 0.2 microM), indicating that acetylcholine generates tonic contraction via increases in both [Ca2+]i and myofilament Ca2+-sensitivity. H2O2 (30 microM) (a) enhanced the acetylcholine-induced tonic (not phasic) increase in [Ca2+]i but attenuated both phases of the acetylcholine-induced contraction and (b) enhanced the high K+-induced increase in [Ca2+]i but did not modify the high K+-induced contraction. In beta-escin-skinned strips, application of acetylcholine in the presence of GTP enhanced the contraction induced by 0.3 microM Ca2+ so that its amplitude became similar to that induced by 1 microM Ca2+. H2O2 (30 microM) attenuated the contraction induced by 0.3 microM Ca2+ (alone or in the presence of acetylcholine) but not those induced by higher concentrations of Ca2+ alone (0.5 microM and 1 microM). These results indicate that H2O2 acts directly on contractile proteins in rabbit tracheal smooth muscle to inhibit the contraction induced by low concentrations of Ca2+ (<0.5 microM). An action of H2O2 that increases [Ca2+]i (and thereby masks this reactive-oxygen-induced inhibition of myofilament Ca2+-sensitivity) is apparent in the presence of high K+ but not of acetylcholine. Thus, in rabbit tracheal smooth muscle H2O2 downregulates myofilament Ca2+-sensitivity more potently during acetylcholine-induced contraction than during high-K+-induced contraction, leading to an effective inhibition of the former contraction.

Hydrogen peroxide increases the phagocytic function of human neutrophils by calcium mobilisation

We have studied the effect of exogenous administration of hydrogen peroxide (H(2)O(2)) on phagocytic activity of human neutrophils. The treatment of cells with increasing concentrations of H(2)O(2) evoke a significant elevation of phagocytic function assayed as phagocytic index, percentage and efficiency; and was similar to that induced by the calcium mobilising agonist formyl-methionyl-leucyl-phenylalanine (fMLP). This stimulatory effect was reduced by pre-treatment of neutrophils with catalase and abolished in neutrophils loaded with the intracellular calcium quelator dimethyl BAPTA. In the absence of extracellular calcium, treatment of cells with H(2)O(2) resulted in a increase in [Ca(2+)]( i ), indicating the release of calcium from intracellular stores. H(2)O(2) abolished the typical calcium release stimulated by the physiological agonist fMLP, while depletion of agonist-sensitive calcium pools by fMLP was able to prevent H(2)O(2)-induced calcium release. We conclude that H(2)O(2) induces calcium release from agonist-sensitive stores and consequently increase the phagocytosis process.

Dose-dependent effect of hydrogen peroxide on calcium mobilization in mouse pancreatic acinar cells

We have employed confocal laser scanning microscopy to investigate how intracellular free calcium concentration ([Ca2+]i) is influenced by hydrogen peroxide (H2O2) in collagenase-dispersed mouse pancreatic acinar cells. In the absence of extracellular calcium, treatment of cells with increasing concentrations of H2O2resulted in an increase in [Ca2+]i, indicating the release of calcium from intracellular stores. Micromolar concentrations of H2O2induced an oscillatory pattern, whereas 1 mmol H2O2/L caused a slow and sustained increase in [Ca2+]i. H2O2abolished the typical calcium release stimulated by thapsigargin or by the physiological agonist cholecystokinin octapeptide (CCK-8). Depletion of either agonist-sensitive or mitochondrial calcium pools was unable to prevent calcium release induced by 1 mmol H2O2/L, but depletion of both stores abolished it. Additionally, lower H2O2concentrations were able to release calcium only after depletion of mitochondrial calcium stores. Treatment with either the phospholipase C inhibitor U-73122 or the inhibitor of the inositol 1,4,5-trisphosphate (IP3) receptor xestospongin C did not modify calcium release from the agonist-sensitive pool induced by 100 µmol H2O2/L, suggesting the involvement of a mechanism independent of IP3 generation. In addition, H2O2reduced amylase release stimulated by CCK-8. Finally, either the H2O2-induced calcium mobilization or the inhibitory effect of H2O2on CCK-8-induced amylase secretion was abolished by dithiothreitol, a sulphydryl reducing agent. We conclude that H2O2at micromolar concentrations induces calcium release from agonist- sensitive stores, and at millimolar concentrations H2O2can also evoke calcium release from the mitochondria. The action of H2O2is mediated by oxidation of sulphydryl groups of calcium ATPases independently of IP3 generation.Key words: hydrogen peroxide, pancreatic acinar cells, intracellular calcium stores, amylase secretion.

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.

The glutathione reductase inhibitor carmustine induces an influx of Ca2+ in PC12 cells

We studied the effects of carmustine (1,3-bis(2-chloroethyl)-1-nitrosourea) on the intracellular Ca(2+) concentration ([Ca(2+)](i)) in PC12 cells using fura-2 fluorescence imaging. Carmustine (100 microM) caused a delayed increase in [Ca(2+)](i) that developed within approximately 3 h. This effect was enhanced in cells that were pretreated with an inhibitor of glutathione (GSH) synthesis, buthionine sulfoximine (BSO, 200 microM, 24 h), and was suppressed in cells that were treated with an antioxidant deferoxamine (50 microM). The carmustine-induced increase in [Ca(2+)](i) was absolutely dependent on the presence of extracellular Ca(2+) and could be inhibited by dihydropyridine blockers of L-type voltage-gated Ca(2+) channels (nimodipine or nitrendipine, 10 microM). The increase in [Ca(2+)](i) was also suppressed in Cl(-)-free solution and in the presence of the Cl(-) channel blockers, indanyloxyacetic acid 94 (IAA-94, 100 microM) and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, 100 microM). The inhibition was complete when the blockers were applied simultaneously with carmustine and was partial when the blockers were applied after the initial increase in [Ca(2+)](i). We conclude that carmustine induces an influx of extracellular Ca(2+) through L-type Ca(2+) channels and that this effect is mediated by oxidative stress that results from the depletion of GSH following the inhibition by carmustine of glutathione reductase.

Distinct roles of Ca2+, calmodulin, and protein kinase C in H2O2-induced activation of ERK1/2, p38 MAPK, and protein kinase B signaling in vascular smooth muscle cells

We have shown earlier that extracellular signal-regulated kinases 1 and 2 (ERK1/2) and protein kinase B (PKB), two key mediators of growth-promoting and proliferative responses, are activated by hydrogen peroxide (H(2)O(2)) in A10 vascular smooth muscle cells (VSMC). In the present studies, using a series of pharmacological inhibitors, we explored the upstream mechanisms responsible for their activation in response to H(2)O(2). H(2)O(2) treatment of VSMC stimulated ERK1/2, p38 mitogen-activated protein kinase (MAPK), and PKB phosphorylation in a dose- and time-dependent fashion. BAPTA-AM and EGTA, chelators of intracellular and extracellular Ca(2+), respectively, inhibited H(2)O(2)-stimulated ERK1/2, p38 MAPK, and PKB phosphorylation. Fluphenazine, an antagonist of the Ca(2+)-binding protein calmodulin, also suppressed the enhanced phosphorylation of ERK1/2, p38 MAPK, and PKB. In contrast, the protein kinase C (PKC) inhibitors Gö 6983 and Rö 31-8220 attenuated H(2)O(2)-induced ERK1/2 phosphorylation, but had no effect on p38 MAPK and PKB phosphorylation. Taken together, these data demonstrate that the activation of Ca(2+)/calmodulin-dependent pathways represents a key component mediating the stimulatory action of H(2)O(2) on ERK1/2, p38 MAPK, and PKB phosphorylation. On the other hand, PKC appears to be an upstream modulator of the increased ERK1/2 phosphorylation, but not of p38 MAPK and PKB in response to H(2)O(2) in VSMC.

Ion dependence of cytotoxicity of carmustine against PC12 cells

Cytotoxicity is a major complication of carmustine (1,3-bis(2-chloroethyl)-1-nitrosourea, BCNU) therapy for treatment of brain tumors and lymphomas. Using the lactate dehydrogenase (LDH) cell death assay in PC12 cells, we studied the role in this phenomenon of transmembrane ion fluxes that could be activated following inhibition by carmustine of glutathione reductase. The cytotoxic effect of carmustine developed during 4-6 h, with the EC50 of 27 microM. It depended on the extracellular Ca2+ concentration and substantially decreased upon Ca2+ removal. An almost complete suppression of toxicity was achieved when, additionally, monovalent cations were also replaced with impermeant organic cations. A similar loss of toxicity occurred in the presence of Ca2+ when extracellular Cl- was replaced with impermeable gluconate. Various blockers of cation and Cl- channels, as well as antioxidants also protected cells from carmustine. We conclude that carmustine toxicity against PC12 cells requires an influx of Ca2+ ions, supposedly through redox-sensitive cation channels.

Cross-talk between cytosolic phospholipase A2 alpha (cPLA2 alpha) and secretory phospholipase A2 (sPLA2) in hydrogen peroxide-induced arachidonic acid release in murine mesangial cells: sPLA2 regulates cPLA2 alpha activity that is responsible for arachidonic acid release

Oxidant stress and phospholipase A2 (PLA2) activation have been implicated in numerous proinflammatory responses of the mesangial cell (MC). We investigated the cross-talk between group IValpha cytosolic PLA2 (cPLA2alpha) and secretory PLA2s (sPLA2s) during H2O2-induced arachidonic acid (AA) release using two types of murine MC: (i). MC+/+, which lack group IIa and V PLA2s, and (ii). MC-/-, which lack groups IIa, V, and IValpha PLA2s. H2O2-induced AA release was greater in MC+/+ compared with MC-/-. It has been argued that cPLA2alpha plays a regulatory role enhancing the activity of sPLA2s, which act on phospholipids to release fatty acid. Group IIa, V, or IValpha PLA2s were expressed in MC-/- or MC+/+ using recombinant adenovirus vectors. Expression of cPLA2alpha in H2O2-treated MC-/- increased AA release to a level approaching that of H2O2-treated MC+/+. Expression of either group IIa PLA2 or V PLA2 enhanced AA release in MC+/+ but had no effect on AA release in MC-/-. When sPLA2 and cPLA2alpha are both present, the effect of H2O2 is manifested by preferential release of AA compared with oleic acid. Inhibition of the ERK and protein kinase C signaling pathways with the MEK-1 inhibitor, U0126, and protein kinase C inhibitor, GF 1092030x, respectively, and chelating intracellular free calcium with 1,2-bis(2-aminophenoyl)ethane-N,N,N',N'-tetraacetic acid-AM, which also reduced ERK1/2 activation, significantly reduced H2O2-induced AA release in MC+/+ expressing either group IIa or V PLA2s. By contrast, H2O2-induced AA release was not enhanced when ERK1/2 was activated by infection of MC+/+ with constitutively active MEK1-DD. We conclude that the effect of group IIa and V PLA2s on H2O2-induced AA release is dependent upon the presence of cPLA2alpha and the activation of PKC and ERK1/2. Group IIa and V PLA2s are regulatory and cPLA2alpha is responsible for AA release.

Selective activation by photodynamic action of cholecystokinin receptor in the freshly isolated rat pancreatic acini

1 Sulphonated aluminium phthalocyanine (SALPC) photodynamic action induces amylase secretion and permanent calcium oscillation in rat pancreatic acinar cells, because of the activation of phospholipase C or signalling proteins upstream. The aim of the present study was to investigate the involvement of muscarinic acetylcholine and cholecystokinin (CCK) receptors. 2 Muscarinic receptor antagonist atropine (10 micro M) blocked amylase secretion induced by bethanechol (100 micro M), and CCK(1) receptor antagonist (S)-N-[1-(2-fluorophenyl)-3,4,6,7-tetrahydor-4-oxo-pyrrolo-[3,2,1-jk][1,4] benzodiazepine-3yl]-1H-indole-2-carboxamide (FK480) (1 micro M) blocked amylase secretion induced by CCK (100 pM). 3 Amylase secretion induced by SALPC photodynamic action was not inhibited when atropine and FK480 were present during photodynamic action. However, addition of FK480 1 micro M after initiation of photodynamic action inhibited photodynamic amylase secretion. Bethanechol (10, 100 micro M) added after photodynamic action resulted in a full secretory response. 4 Atropine (10 nM) abolished calcium oscillation induced by bethanechol (5 micro M), and FK480 (10 nM) blocked calcium oscillation induced by CCK (10 pM). 5 Atropine up to 10 micro M was without effect on Ca(2+) oscillation triggered by photodynamic action, but these oscillations were abolished by FK480 (10 nM). FK480 (10 nM) had no effect on calcium oscillations induced by bethanechol (5 micro M). Bethanechol 5 micro M, added after FK480 blockade of photodynamic calcium oscillation, still triggered regular calcium oscillation. 6 It is concluded that SALPC photodynamic action selectively and permanently activates CCK receptor in rat pancreatic acini. Such permanent and selective modulation of signalling proteins has important implications for the treatment of pancreatitis, prion diseases, and neurodegenerative disorders.

A novel mechanism by which hydrogen peroxide decreases calcium sensitivity in airway smooth muscle

The purpose of this study was to test the hypothesis that H(2)O(2) decreases the amount of force produced by a given intracellular Ca(2+) concentration (i.e., the Ca(2+) sensitivity) in airway smooth muscle (ASM) in part by mechanisms independent of changes in regulatory myosin light chain (rMLC) phosphorylation. A new preparation was developed and validated in which canine ASM strips were first exposed to H(2)O(2) and then permeabilized with 10% Triton X-100 to assess the persistent effects of H(2)O(2) on Ca(2+) sensitivity. Experiments in which H(2)O(2) was administered before permeabilization revealed a novel mechanism that contributed to reduced Ca(2+) sensitivity independently of changes in rMLC phosphorylation, in addition to an rMLC phosphorylation-dependent mechanism. The mechanism depended on factors not available in the permeabilized ASM strip or in the buffer to which the strip was exposed, since there was no effect when H(2)O(2) was added to permeabilized strips. H(2)O(2) treatment of a maximally thiophosphorylated purified myosin subfragment (heavy meromyosin) significantly reduced actomyosin ATPase activity, suggesting one mechanism by which the phosphorylation-independent reduction in Ca(2+) sensitivity may occur.

Increase in cytosolic Ca2+ levels through the activation of non-selective cation channels induced by oxidative stress causes mitochondrial depolarization leading to apoptosis-like death in Leishmania donovani promastigotes

Reactive oxygen species are important regulators of protozoal infection. Promastigotes of Leishmania donovani, the causative agent of Kala-azar, undergo an apoptosis-like death upon exposure to H2O2. The present study shows that upon activation of death response by H2O2, a dose- and time-dependent loss of mitochondrial membrane potential occurs. This loss is accompanied by a depletion of cellular glutathione, but cardiolipin content or thiol oxidation status remains unchanged. ATP levels are reduced within the first 60 min of exposure as a result of mitochondrial membrane potential loss. A tight link exists between changes in cytosolic Ca2+ homeostasis and collapse of the mitochondrial membrane potential, but the dissipation of the potential is independent of elevation of cytosolic Na+ and mitochondrial Ca2+. Partial inhibition of cytosolic Ca2+ increase achieved by chelating extracellular or intracellular Ca2+ by the use of appropriate agents resulted in significant rescue of the fall of the mitochondrial membrane potential and apoptosis-like death. It is further demonstrated that the increase in cytosolic Ca2+ is an additive result of release of Ca2+ from intracellular stores as well as by influx of extracellular Ca2+ through flufenamic acid-sensitive non-selective cation channels; contribution of the latter was larger. Mitochondrial changes do not involve opening of the mitochondrial transition pore as cyclosporin A is unable to prevent mitochondrial membrane potential loss. An antioxidant like N-acetylcysteine is able to inhibit the fall of the mitochondrial membrane potential and prevent apoptosis-like death. Together, these findings show the importance of non-selective cation channels in regulating the response of L. donovani promastigotes to oxidative stress that triggers downstream signaling cascades leading to apoptosis-like death.

Effects of reactive oxygen species on actin filament polymerisation and amylase secretion in mouse pancreatic acinar cells

The present study investigates the effect of reactive oxygen species (ROS) on actin filament reorganisation and its relevance to exocytosis in pancreatic acinar cells. Treatment of pancreatic acini with cholecystokinin (CCK-8) induced spatial and temporal changes in actin filament reorganisation with an initial depolymerisation of the apical actin barrier followed by an increase in the actin filament content in the subapical area leading to amylase release. Hydrogen peroxide (H(2)O(2)) increased actin filament content and potentiated the polymerizing effects of CCK-8 in these cells but abolished the disruption of the apical actin layer and amylase release induced by CCK-8. Similar to CCK-8, ROS generated by the oxidation of hypoxanthine (HX) with xanthine oxidase (XOD) induced an initial decrease in actin filaments located under the apical membrane followed by a smaller increase in the content of actin filaments in the subapical area. XOD-generated ROS are able to increase amylase release in pancreatic acini although combination with CCK-8 leads to abnormal exocytosis. We provide evidence that indicates that CCK-8- and ROS-induced actin reorganisation is entirely dependent on Ca(2+) mobilisation and independent of PKC activation. The regulation of the actin cytoskeleton by ROS might be involved in radical-induced cell injury in pancreatic acinar cells.

Mechanism of vascular smooth muscle cells activation by hydrogen peroxide: role of phospholipase C gamma

BACKGROUND

Hydrogen peroxide (H2O2) formation is a critical factor in processes involving ischaemia/ reperfusion. However, the precise mechanism by which reactive oxygen species (ROS) induce vascular damage are insufficiently known. Specifically, activation of phospholipase C gamma (PLCgamma) is a probable candidate pathway involved in vascular smooth muscle cells (VSMC) activation by H2O2.

METHODS

The activation of human venous VSMC was measured as cytosolic free calcium mobilization, shape change and protein phosphorylation, focusing on the role of tyrosine phosphorylation-activated PLCgamma.

RESULTS

The exposure of VSMC to exogenous H2O2 caused a rapid increase in cytosolic free calcium concentration ([Ca2+]i), and induced a significant VSMC shape change. Both effects were dependent on a tyrosine kinase-mediated mechanism, as determined by the blockade of short-term treatment of VSMC with the protein tyrosine kinase inhibitor, genistein. Giving further support to the putative role of phospholipase C (PLC)-dependent pathways, the [Ca2+]i and VSMC shape change response were equally inhibited by the specific PLC blocker, 1-(6-((17-beta-methoxyestra-1,3,5(10)trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122). In addition, U73122 had a protective effect against the deleterious action (24 h) of H2O2 on non-confluent VSMC. As a further clarification of the specific pathway involved, the exposure to H2O2 significantly stimulated the tyrosine phosphorylation of PLCgamma with a concentration- and time-profile similar to that of [Ca(2+)](i) mobilization.

CONCLUSIONS

The present study reveals that H(2)O(2) activates PLCgamma on VSMC through tyrosine phosphorylation and that this activation has a major role in rapid [Ca(2+)](i) mobilization, shape-changing actions and damage by H(2)O(2) in this type of cells. These findings have direct implications for understanding the mechanisms of the vascular actions of H(2)O(2) and may help to design pharmacologically protective strategies.

ERK and p38 MAP kinase are involved in arachidonic acid release induced by H(2)O(2) and PDGF in mesangial cells

Increased prostaglandin production is implicated in the pathogenesis of glomerular disease. With this consideration, we examined the combined effects of reactive oxygen species and platelet-derived growth factor (PDGF), which might initiate glomerular dysfunction, on arachidonic acid release and cytosolic phospholipase A(2) (cPLA(2)) activation in rat mesangial cells. H(2)O(2)-induced release of arachidonic acid was enhanced by PDGF, which by itself had little effect on the release, and the enhancement was completely inhibited by a cPLA(2) inhibitor. The phosphorylation of cPLA(2), extracellular signal-regulated kinase (ERK), and p38 mitogen-activated protein (MAP) kinase was upregulated by H(2)O(2) or PDGF alone and except for ERK was enhanced further by the two in combination. The release of arachidonic acid induced by PDGF together with H(2)O(2) was inhibited partially by an inhibitor of ERK or p38 MAP kinase and completely when the two inhibitors were combined; the inhibitory pattern was similar to that for the phosphorylation of cPLA(2). These results suggest that the ERK and p38 MAP kinase pathways are involved in the increase in cPLA(2) activation and arachidonic acid release induced by PDGF together with H(2)O(2).

Reactive oxygen metabolites induce a biphasic contractile response in microvascular lung pericytes

BACKGROUND

The changes in microvascular permeability characteristic of postinjury inflammation and sepsis may involve dysfunctional regulatory mechanisms at the capillary level. Pericytes, positioned abluminal to microvascular endothelium may, by their contractility, contribute to this regulation. Reactive oxygen metabolites (ROMs), well-known participants in lung inflammation, may exert an effect on pericytes, leading to changes in permeability and adult respiratory distress syndrome. This study investigates the effect of ROMs and antioxidants in an established in vitro assay of pericyte contractility.

METHODS

Rat lung pericytes were cultured on collagen gel matrices. After exposure to the ROMs, the surface area of the collagen disks was digitally quantified (an integrated measure of cellular contraction) at 10 and 30 minutes. The cells were exposed to hydrogen peroxide and pyrogallol at 10, 100, and 1,000 micromol/L. Antioxidant effects of catalase (100 micromol/L), superoxide dismutase (100 micromol/L), and pretreatment with vitamin E (1 mmol/L) were quantified.

RESULTS

Hydrogen peroxide and pyrogallol induced concentration-dependent relaxation at 10 minutes. Conversely, concentration-dependent contraction was seen at 30 minutes. Catalase completely attenuated both responses, whereas superoxide dismutase had no effect. Vitamin E had no effect at 10 minutes but partially attenuated the contraction seen at 30 minutes.

CONCLUSION

ROMs are capable of producing early relaxation and late contraction in cultured lung pericytes. Whereas catalase attenuates both responses, membrane-bound vitamin E only partially attenuates late contraction. This suggests two separate mechanisms: early physiologic relaxation through signaling pathways affecting actin/myosin tone, and late membrane damage causing contraction. Either pathway may cause dysfunction in pulmonary capillary fluid regulation.

Effects of antioxidants on calcium signal induced by cholecystokinin in mouse pancreatic acinar cells

Digital imaging fluorescence microscopy was used to study the effect of two antioxidants, N-acetyl-cysteine (NAC) and glutathione, on the cytosolic free calcium concentration ([Ca2+]i) induced by cholecystokinin-octapeptide (CCK-8) of mouse pancreatic acinar cells. When acinar cells were preincubated with either NAC or glutathione, subsequent stimulation with CCK-8 in the presence of each antioxidant had no significant effect on the typical pattern of [Ca2+]i transient evoked by the gastrointestinal hormone. However, application of NAC to acinar cells pretreated for 60 min with the same antioxidant, strongly blocked the oscillatory pattern initiated by CCK-8, inhibiting both amplitude and frequency of calcium oscillations. By contrast, glutathione had no effect on the oscillatory pattern evoked by CCK-8. The present results allow us to speculate that during [Ca2+]i oscillation there is a production of oxidants that facilitate oscillations by enhancing release of calcium from internal stores.

Inhibitory effects of methanol extract of seeds of Job's Tears (Coix lachryma-jobi L. var. ma-yuen) on nitric oxide and superoxide production in RAW 264.7 macrophages

Overproduction of nitric oxide (NO) or superoxide (O2-) by activated macrophages is known to be involved in acute or chronic inflammation. The seeds of Job's Tears (Coix lachryma-jobi L. var. ma-yuen) have been used as anti-inflammatory medicine and health food. However, it is still unclear how the seeds show anti-inflammatory properties. Using murine macrophage-like RAW 264.7 cells, we tried to know whether the overproduction of NO and O2 by activated macrophages could be prevented by the methanol (MeOH) extract of the seeds of Job's Tears. RAW 264.7 cells were activated with interferon-gamma plus lipopolysaccharide to produce NO and with pholbol ester to produce O2-. The MeOH extract showed marked inhibition of NO production by activated RAW 264.7 cells in a dose-dependent manner via suppression of inducible NO synthase mRNA expression. The MeOH extract also showed inhibition of O2- production by activated RAW 264.7 cells in dose- and time-dependent manners, possibly by interfering with NADPH oxidase machinery of macrophages. Collectively, these results demonstrate that the MeOH extract of the seeds of Job's Tears shows anti-inflammatory properties which may, in part, involve an inhibition of NO and O2- production by activated macrophages.

TNF-alpha and IL-1alpha induce apoptosis in subconfluent rat mesangial cells. Evidence for the involvement of hydrogen peroxide and lipid peroxidation as second messengers

Apoptosis of mesangial cells (MC) plays a role in glomerulonephritis (GN). In this study we investigated cytokine-induced apoptosis of cultured rat MC by morphological and biochemical features. TNF-alpha and IL-1alpha induced apoptosis in rat MC in a time- and concentration-dependent fashion. RT-PCR experiments revealed that MC express the TNF-receptor 1 (p60) gene constitutively. TNF-alpha as well as IL-1alpha stimulated the production of reactive oxygen species (ROS) and induced lipid peroxidation. Coincubation with catalase inhibited TNF-alpha and IL-1alpha induced apoptosis as well as lipid peroxidation. TNF-alpha, but not IL-1alpha increased the expression of c-jun. These results provide evidence that TNF-alpha and IL-1alpha induce apoptosis in rat MC with hydrogen peroxide and lipid peroxidation as second messengers. Increased c-jun expression may be a downstream intracellular signal of TNF-alpha-, but not IL-1alpha-induced apoptosis.

Effects of cumene hydroperoxide on cellular cation composition in frog kidney proximal tubular cells

Effects of cumene hydroperoxide were studied on the peritubular membrane potential and cellular cation composition in frog kidney proximal tubular cells. After perfusion of isolated frog kidneys for 30 min with 1.3x10(-4) mol l(-1) cumene hydroperoxide Ringer solution, the peritubular membrane potential gradually declined. The ouabain-like effects were demonstrated on cell Na and K activities after 1 h of perfusion with cumene hydroperoxide. The peritubular apparent transference number for potassium was decreased. Intracellular pH was not altered in the presence of cumene hydroperoxide. Intracellular free Ca(2+) concentration increased slowly and moderately. The concentration of the malondialdehyde in the kidney homogenates, measured as an index of lipid peroxidation, was increased. A previously observable effect of cumene hydroperoxide on the peritubular membrane potential was prevented by oxygen radical scavengers.

Hydrogen peroxide decreases Ca(2+) sensitivity in airway smooth muscle by inhibiting rMLC phosphorylation

The purpose of this study was to determine the mechanism by which hydrogen peroxide (H(2)O(2)), an important inflammatory mediator, relaxes canine tracheal smooth muscle (CTSM). H(2)O(2) caused concentration-dependent relaxations of CTSM strips contracted with ACh or isotonic KCl [EC(50) of 0.24 +/- 0.04 (SE) and 0.23 +/- 0.04 mM, respectively]. Indomethacin (10 microM) decreased the sensitivity of both KCl- and ACh-contracted strips to H(2)O(2). H(2)O(2) increased intracellular cAMP levels, an increase that was abolished by indomethacin. H(2)O(2) did not affect intracellular cGMP levels. In strips treated with indomethacin and contracted with ACh or isotonic KCl, H(2)O(2)-evoked relaxations were accompanied by increases in intracellular Ca(2+) concentration and decreases in regulatory myosin light chain phosphorylation. We conclude that H(2)O(2) decreases Ca(2+) sensitivity in CTSM by decreasing regulatory myosin light chain phosphorylation through inhibition of myosin light chain kinase and/or activation of smooth muscle protein phosphatases.

Growth stimulation versus induction of cell quiescence by hydrogen peroxide in prostate tumor spheroids is encoded by the duration of the Ca(2+) response

With increasing size, multicellular prostate tumor spheroids develop regions of quiescent, multidrug-resistant cells expressing the cyclin-dependent kinase inhibitor p27(kip1). Treatment of small (diameter 60 +/- 20 micrometer) spheroids with 200 microM hydrogen peroxide (H(2)O(2)) resulted in cell cycle arrest owing to up-regulation of p27(kip1) and down-regulation of the transcription factor c-Fos. Incubation with 100 nM-1 microM H(2)O(2) led to up-regulation of c-Fos and enhanced tumor growth. Growth stimulation was inhibited by bisindolylmaleimide I, indicating a role for protein kinase C in the signaling cascade that involved the mitogen-activated protein kinase members MEK1,2, ERK1, -2, and c-Jun N-terminal kinase. Changes in Ca(2+) influx underlined the differential effects of H(2)O(2). Incubation with 200 microM H(2)O(2) released [Ca(2+)](i) from intracellular stores followed by prolonged Ca(2+) influx. Inhibition of influx by Ca(2+)-free media or Ni(2+), La(3+), Mn(2+) and SKF-96365 prevented the induction of quiescence and stimulated spheroid growth. Consequently, treatment with 200 microM H(2)O(2) in Ca(2+)-free media down-regulated p27(kip1) and increased Fos protein. ATP exerted effects comparably to those observed with H(2)O(2). Encoding growth stimulation by [Ca(2+)](i) release and induction of cell quiescence by prolonged Ca(2+) influx may provide a general mechanism for the control of tumor growth.

Hydrogen peroxide activates ion currents in rat mesangial cells

BACKGROUND

Hydrogen peroxide (H2O2) is an important mediator of glomerular injury, which induces proliferation and cell contraction in mesangial cells. The aim of this study was to investigate whether and which ion currents are activated during the early cellular responses to H2O2, and to study possible mechanisms of their activation.

METHODS

The effect of H2O2 on membrane voltage of mesangial cells in short-term culture was investigated with the patch clamp technique in the fast whole cell configuration.

RESULTS

H2O2 contracted mesangial cells and induced a concentration-dependent biphasic membrane voltage response. One hundred micromol/liter H2O2 led to a hyperpolarization of mesangial cells from -45 +/- 1 to -55 +/- 1 mV, which was followed by a sustained depolarization to -20 +/- 3 mV. The hyperpolarization induced by H2O2 was completely blocked by the K+ channel blocker Ba2+. In the presence of a low extracellular Cl- concentration (32 mmol/liter), the depolarization induced by H2O2 was significantly increased. The H2O2-induced depolarization was inhibited by 100 micromol/liter of the disulfide-reducing agent dithiothreitol, whereas higher concentrations of dithiothreitol (1 mmol/liter) were required to partially inhibit the hyperpolarization. Protein kinase C inhibitors blocked the H2O2-induced depolarization, but not the hyperpolarization.

CONCLUSIONS

The data indicate that H2O2 leads to a biphasic membrane voltage response in mesangial cells: an initial transient hyperpolarization, which is due to the activation of a K+ conductance, and a subsequent depolarization, which is, at least in part, due to the activation of a Cl- conductance. The oxidation of thiol groups by H2O2 is involved in the membrane voltage response, and the depolarization may be regulated by protein kinase C.

The concept of glomerular self-defense

The balance between local offense factors and defense machinery determines the fate of tissue injury: progression or resolution. In glomerular research, the most interest has been on the offensive side, for example, the roles of leukocytes, platelets, complement, cytokines, eicosanoids, and oxygen radical intermediates. There has been little focus on the defensive side, which is responsible for the attenuation and resolution of disease. The aim of this review is to address possible mechanisms of local defense that may be exerted during glomerular injury. Cytokine inhibitors, proteinase inhibitors, complement regulatory proteins, anti-inflammatory cytokines, anti-inflammatory eicosanoids, antithrombotic molecules, and extracellular matrix proteins can participate in the extracellular and/or cell surface defense. Heat shock proteins, antioxidants, protein phosphatases, and cyclin kinase inhibitors may contribute to the intracellular defense. This article outlines how the glomerulus, when faced with injurious cells or exposed to pathogenic mediators, defends itself via the intrinsic machinery that is brought into play in resident glomerular cells.

Interference of H2O2 with stimulus-secretion coupling in mouse pancreatic beta-cells

1. We have reported previously that in mouse pancreatic beta-cells H2O2 hyperpolarizes the membrane and increases the ATP-sensitive K+ current recorded in the perforated patch configuration of the patch-clamp technique. The present study was undertaken to elucidate the underlying mechanisms. 2. The intracellular ATP concentration measured by chemoluminescence was reduced by H2O2. The ADP concentration increased in parallel during the first 10 min, resulting in a pronounced decrease in the ATP/ADP ratio. 3. Consistent with these results, glucose-stimulated insulin secretion from isolated islets was inhibited by H2O2. 4. Membrane hyperpolarization measured with intracellular microelectrodes in intact islets and inhibition of insulin secretion were counteracted by tolbutamide, indicating that the channels are still responsive to inhibitors and that the ATP concentration is not too low to trigger exocytosis. However, the sensitivity of the beta-cells to tolbutamide was reduced after treatment with H2O2. 5. H2O2 increased the intracellular Ca2+ activity ([Ca2+]i) in a biphasic manner. A first transient rise in [Ca2+]i due to mobilization of Ca2+ from intracellular stores was followed by a sustained increase, which was at least partly dependent on Ca2+ influx. The first phase seems to reflect Ca2+ mobilization from mitochondria. 6. Our results demonstrate that H2O2 interferes with glucose metabolism, which influences the membrane potential and ATP-sensitive K+ current via the intracellular concentration of ATP. These events finally lead to an inhibition of insulin secretion despite an increase in [Ca2+]i.

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.

Rearrangements of the cytoskeleton and cell contacts induce process formation during differentiation of conditionally immortalized mouse podocyte cell lines

Mature podocytes are among the most complex differentiated cells and possess a highly branched array of foot processes that are essential to glomerular filtration in the kidney. Such differentiated podocytes are unable to replicate and culturing of primary podocytes results in rapid growth arrest. Therefore, conditionally immortalized mouse podocyte clones (MPC) were established, which are highly proliferative when cultured under permissive conditions. Nonpermissive conditions render the majority of MPC cells growth arrested within 6 days and induce many characteristics of differentiated podocytes. Both proliferating and differentiating MPC cells express the WT-1 protein and an ordered array of actin fibers and microtubules extends into the forming cellular processes during differentiation, reminiscent of podocyte processes in vivo. These cytoskeletal rearrangements and process formation are accompanied by the onset of synaptopodin synthesis, an actin-associated protein marking specifically differentiated podocytes. In addition, focal contacts are rearranged into an ordered pattern in differentiating MPC cells. Most importantly, electrophysiological studies demonstrate that differentiated MPC cells respond to the vasoactive peptide bradykinin by changes in intracellular calcium concentration. These results suggest a regulatory role of podocytes in glomerular filtration. Taken together, these studies establish that conditionally immortalized MPC cells retain a differentiation potential similar to podocytes in vivo. Therefore, the determinative steps of podocyte differentiation and process formation are studied for the first time using an inducible in vitro model.

Angiotensin II increases the cytosolic calcium activity in rat podocytes in culture

In the glomerulus, angiotensin II (Ang II) reduces the ultrafiltration coefficient and enhances the filtration of macromolecules. During glomerular injury, inhibition of the renin-angiotensin system by angiotensin-converting-enzyme inhibitors reduces proteinuria and retards the progression to end-stage renal insufficiency. The mechanisms by which Ang II modulates glomerular function are still a matter of investigation. To study whether Ang II may regulate the cytosolic calcium activity ([Ca2+]i) in podocytes, these cells were propagated in short-term culture and the effect of Ang II was examined with the Fura-2 microfluorescence technique in single podocytes. The cellular identity of cultured podocytes was proven by the expression of WT-1 and pp44, specific antibodies against podocytes in vivo. Ang II led to a concentration-dependent, reversible and slow increase of [Ca2+]i with an EC50 of 3 nmol/liter Ang II (N = 229). Ten nmol/liter Ang II increased [Ca2+]i from 41 +/- 9 to 260 +/- 34 nmol/liter (N = 210). In a solution with an extracellular reduced Ca2+ concentration of 10 micromol/liter, Ang II-mediated [Ca2+]i increase was significantly reduced by 60 +/- 20% (N = 12), indicating that the [Ca2+]i increase was due to a Ca2+ influx from the extracellular space and a release of Ca2+ from intracellular stores. Flufenamate, an inhibitor of non-selective ion channels, significantly inhibited Ang II-mediated increase of [Ca2+]i (IC50 = 20 micromol/liter, N = 29), whereas the L-type Ca2+ channel blocker nicardipine even in high concentrations of > 1 micromol/liter had only a small inhibitory effect. The AT1 receptor antagonist losartan inhibited Ang II-mediated [Ca2+]i increase with an IC50 of about 0.3 nmol/liter (N = 35). The data suggest that Ang II increases [Ca2+]i in podocytes by an influx of Ca2+ through non-selective channels and by a release of Ca2+ from intracellular stores. The effect of Ang II is mediated via an AT1 receptor.