Reversible and irreversible oxidant injury to PC12 cells by hydrogen peroxide

Isolation, Bioactivity, and Molecular Docking of a Rare Gastrodin Isocitrate and Diverse Parishin Derivatives from Gastrodia elata Blume

Gastrodia elata Blume (G. elata) is a well-known medicine food homology plant widely used in treating neurological disorders such as Alzheimer's disease (AD). Here, undiscovered gastrodin derivatives were systematically studied. Seven novel gastrodin derivatives (1-7), including a unique gastrodin isocitrate (1) and six differently substituted parishin derivatives (2-7), were isolated. Structural identification was mainly based on 1D and 2D NMR data, high-resolution ESI-MS data, and HPLC analysis. Notably, the stereochemistry of 1 was further elucidated by ECD calculations. Compounds 1 and 6 showed neuroprotective effects on the H2O2-induced PC12 cell injury model. Molecular docking analysis exhibited that 1 and 6 had good affinities with three popular AD-related targets. These findings not only enriched the chemical diversity but also revealed potential active components in G. elata.

Additive Protective Effects of Delayed Mild Therapeutic Hypothermia and Antioxidants on PC12 Cells Exposed to Oxidative Stress

Mild therapeutic hypothermia is protective against several cellular stresses, but the mechanisms underlying this protection are not completely resolved. In the present study, we used an in vitro model to investigate whether therapeutic hypothermia at 33°C applied following a peroxide-induced oxidative stress would protect PC12 cells. A 1-hour exposure to tert-butyl peroxide increased cell death measured 24 hours later. This cell death was dose-dependent in the range of 100-1000 μM tert-butyl peroxide with ∼50% cell death observed at 24 hours from 500 μM peroxide exposure. Cell survival/death was measured with an alamarBlue viability assay, and propidium iodide/Hoechst imaging for counts of living and dead cells. Therapeutic hypothermia at 33°C applied for 2 hours postperoxide exposure significantly increased cell survival measured 24 hours postperoxide-induced stress. This protection was present even when delayed hypothermia, 15 minutes after the peroxide washout, was applied. Addition of any of the three FDA-approved antioxidants (Tempol, EUK134, Edaravone at 100 μM) in combination with hypothermia improved cell survival. With the therapeutic hypothermia treatment, a significant downregulation of caspases-3 and -8 and tumor necrosis factor-α was observed at 3 and 24 hours poststress. Consistent with this, a cell-permeable pan-caspase inhibitor Z-VAD-FMK applied in combination with hypothermia significantly increased cell survival. Overall, these results suggest that the antioxidants quenching of reactive oxygen species likely works with hypothermia to reduce mitochondrial damage and/or apoptotic mechanisms. Further studies are required to confirm and extend these results to other cell types, including neuronal cells, and other forms of oxidative stress as well as to optimize the critical parameters of hypothermia treatment such as target temperature and duration.

Design, synthesis and pharmacological evaluation of (E)-3,4-dihydroxy styryl sulfonamides derivatives as multifunctional neuroprotective agents against oxidative and inflammatory injury

A novel class of (E)-3,4-dihydroxy styryl sulfonamides and their 3,4-diacetylated derivatives as caffeic acid phenethyl ester (CAPE) analogs was designed and prepared for improving stability and solubility of the lead compound. Their neuroprotective properties were assessed by several models. The results showed that target compounds displayed positive free radical quenching abilities, superior to that of CAPE. Compounds 6j-k and 7j-k demonstrated remarkable protection effects against damage induced by hydrogen peroxide which were apparently stronger than that of CAPE. Most of target compounds could inhibit nitric oxide production. Additionally, target compounds showed high blood-brain barrier permeability.

Cytotoxic, cytoprotective and antioxidant effects of isolated phenolic compounds from fresh ginger

Twenty-nine phenolic compounds were isolated from the root bark of fresh (Yunnan) ginger and their structures fully characterized. Selected compounds were divided into structural categories and twelve compounds subjected to in-vitro assays including DPPH radical scavenging, xanthine-oxidase inhibition, monoamine oxidase inhibition, rat-brain homogenate lipid peroxidation, and rat pheochromocytoma PC12 cell and primary liver cell viability to determine their antioxidant and cytoprotective properties. Isolated compounds were also tested against nine human tumor cell lines to characterize anticancer potency. Several diarylheptanoids and epoxidic diarylheptanoids were effective DPPH radical scavengers and moderately effective at inhibiting xanthine oxidase. An enone-dione analog of 6-shogaol (compound 2) was isolated and identified to be most effective at protecting PC12 cells from H₂O₂-induced damage. Almost all tested compounds inhibited lipid peroxidation. Three compounds, 6-shogaol, 10-gingerol and an enone-diarylheptanoid analog of curcumin (compound 6) were identified to be cytotoxic in cell lines tested, with KB and HL60 cells most susceptible to 6-shogaol and the curcumin analog with IC₅₀<10 μM. QSAR analysis revealed cytotoxicity was related to compound lipophilicity and chemical reactivity. In conclusion, we observed distinct compounds in fresh ginger to have biological activities relevant in diseases associated with reactive oxygen species.

Design, synthesis, and examination of neuron protective properties of alkenylated and amidated dehydro-silybin derivatives

A series of C7-O- and C20-O-amidated 2,3-dehydrosilybin (DHS) derivatives ((+/-)-1a-f and (+/-)-2), as well as a set of alkenylated DHS analogues ((+/-)-4a-f), were designed and de novo synthesized. A diesteric derivative of DHS ((+/-)-3) and two C23 esterified DHS analogues ((+/-)-5a and (+/-)-5b) were also prepared for comparison. The cell viability of PC12 cells, Fe(2+) chelation, lipid peroxidation (LPO), free radical scavenging, and xanthine oxidase inhibition models were utilized to evaluate their antioxidative and neuron protective properties. The study revealed that the diether at C7-OH and C20-OH as well as the monoether at C7-OH, which possess aliphatic substituted acetamides, demonstrated more potent LPO inhibition and Fe(2+) chelation compared to DHS and quercetin. Conversely, the diallyl ether at C7-OH and C20-OH was more potent in protection of PC12 cells against H(2)O(2)-induced injury than DHS and quercetin. Overall, the more lipophilic alkenylated DHS analogues were better performing neuroprotective agents than the acetamidated derivatives. The results in this study would be beneficial for optimizing the therapeutic potential of lignoflavonoids, especially in neurodegenerative disorders such as Alzheimer's and Parkinson's disease.

TNF alpha-mediated disruption of spermatogenesis in response to Sertoli cell injury in rodents is partially regulated by MMP2

Mono-(2-ethylhexyl) phthalate (MEHP)-induced Sertoli cell injury in peripubertal rodents results in the stimulation of germ cell apoptosis through an interaction of FAS/FASL between these two cell types. During this peripubertal period, an early spike in the incidence of germ cell apoptosis occurs during the first wave of spermatogenesis and is essential for the development of functional spermatogenesis in adults. Our previous observations revealed that soluble tumor necrosis factor alpha (sTNFA) released by germ cells after MEHP exposure consequently resulted in a robust induction of FASL by Sertoli cells. Metalloproteinases (MPs) are essential for processing the TNFA precursor to its soluble form and its ability to bind to TNFRSF1A. The activity of MPs is regulated by the tissue inhibitors of MPs (TIMPs) family. Herein we report that TIMP2 is predominately expressed in Sertoli cells and that protein levels decrease in a time-dependent manner after MEHP exposure. The secretion of matrix MP 2 (MMP2) in primary rat Sertoli cell-germ cell cocultures is induced after MEHP exposure, and its activity increases in a time-dependent manner. The addition of SB-3CT, a specific gelatinase inhibitor, decreases the activity of MMP2 and significantly reduces MEHP-enhanced sTNFA production in primary cocultures. In vivo challenges with SB-3CT decrease sTNFA and reduce MEHP-induced testicular germ cell apoptosis. In primary cocultures, MEHP exposure causes a 9.46-fold increase in sTNFA, while the addition of recombinant MMP2 protein results in a 5.4-fold increase in sTNFA, suggesting that MEHP-induced MMP2 is in part responsible for the activation of TNFA in the testis. Taken together, these observations indicate the distinct role of specific MPs in response to toxicant-induced Sertoli cell injury, providing further insights into the mechanism by which Sertoli cells control the sensitivity of germ cells to undergo apoptosis.

Transcriptional regulation of FasL expression and participation of sTNF-alpha in response to sertoli cell injury

The Fas/FasL signaling pathway has previously been demonstrated to be critical for triggering germ cell apoptosis in response to mono-(2-ethylhexyl)phthalate (MEHP)-induced Sertoli cell injury. Although Sertoli cells ubiquitously express the FasL protein, MEHP-induced germ cell apoptosis appears to tightly correlate with increased levels of Sertoli cell FasL. Here we characterize the transcriptional regulation of the murine FasL gene in Sertoli cells after MEHP exposure. A serial deletion strategy for 1.5 kb of the 5'-upstream activating sequence of the FasL promoter was used to determine transcriptional activity in response to MEHP. Luciferase activity of the FasL promoter in the rat Sertoli cell line ASC-17D revealed that two regions, -500 to -324 and -1250 to -1000, were necessary to drive the inducible transcription of FasL. Sequence analysis of these two regions revealed two cis-regulatory elements, NF-kappaB and Sp-1. By site-directed mutagenesis, electrophoretic mobility shift and chromatin immunoprecipitation assays, it was confirmed that MEHP-induced FasL expression is enhanced through the transcriptional regulation of both NF-kappaB and Sp-1. Experiments performed both in vitro and in vivo revealed that MEHP exposure results in an increased production of sTNF-alpha and that sTNF-alpha-mediated NF-kappaB activation causes robust increases in FasL levels in both the ASC-17D Sertoli cell line and in primary rat Sertoli cell/germ cell co-cultures. In the seminiferous epithelium, Sertoli cells express TNFR1, whereas germ cells produce TNF-alpha. Therefore, sTNF-alpha released by germ cells after MEHP-induced Sertoli cell injury acts upon Sertoli cell TNFR1 and activates NF-kappaB and Sp-1 that consequently causes a robust induction of FasL expression. These novel findings point to a potential "feed-forward" signaling mechanism by which germ cells prompt Sertoli cells to trigger their apoptotic elimination.

The Cu(II)-reductase NADH dehydrogenase-2 of Escherichia coli improves the bacterial growth in extreme copper concentrations and increases the resistance to the damage caused by copper and hydroperoxide

NADH dehydrogenase-2 (NDH-2) from Escherichia coli respiratory chain is a membrane-bound cupric-reductase encoded by ndh gene. Here, we report that the respiratory system of a ndh deficient strain suffered a faster inactivation than that of the parental strain in the presence of tert-butyl hydroperoxide due to endogenous copper. The inactivation was similar for both strains when copper concentration increased in the culture media. Furthermore, several ndh deficient mutants grew less well than the corresponding parental strains in media containing either high or low copper concentrations. A mutant strain complemented with ndh gene almost recovered the parental phenotype for growing in copper limitation or excess. Then, NDH-2 gives the bacteria advantages to diminish the susceptibility of the respiratory chain to damaging effects produced by copper and hydroperoxides and to survive in extreme copper conditions. These results suggest that NDH-2 contributes in the bacterial oxidative protection and in the copper homeostasis.

Enhanced neuronal protection from oxidative stress by coculture with glutamic acid decarboxylase-expressing astrocytes

Astrocytes expressing glutamic acid decarboxylase GAD67 directed by the glial fibrillary acidic protein promoter were shown to provide enhanced protection of PC12 cells from H(2)O(2) treatment and serum deprivation in the presence of glutamate. In addition, they protected non-differentiated, but not differentiated, embryonic rat cortical neurons from glutamate toxicity. Glutamic acid decarboxylase (GAD)-expressing astrocytes showed increased glutathione synthesis and release compared to control astrocytes. These changes were due to GAD transgene expression, as transient expression of a GAD antisense plasmid resulted in partial suppression of the increase in glutathione release. In addition to the previously demonstrated increases in NADH and ATP levels and lactate release, GAD-expressing astrocytes show increased antioxidant activity, explaining their ability to protect neurons from various injuries.

Reduction of H2O2-evoked, intracellular calcium increases in the rat N18-RE-105 neuronal cell line by pretreatment with an electrophilic antioxidant inducer

Pretreatment of the neuronal cell line N18-RE-105 with the antioxidant enzyme inducer dimethyl fumarate (DMF) reduced cell death elicited by H2O2 (50 mM for 1 h) as measured 24 h after H2O2 washout. Oxidants like H2O2 may contribute to cell death by increasing intracellular ionized calcium ([Ca2+]i), suggesting that DMF may in part confer protection by altering H2O2-induced [Ca2+]i signals. To examine this possibility, we measured [Ca2+]i of fura-2-loaded cultures of DMF- and vehicle-pretreated cells during H2O2 superfusion. H2O2 exposure induced a delayed [Ca2+]i increase that was significantly lower in DMF-pretreated cells than controls. Elevation of extracellular cystine also reduced the H2O2 induced [Ca2+]i elevation. Thus, antioxidant upregulation may contribute to protection during oxidative stress by stabilizing [Ca2+]i. However, since oxidative stress may induce cytotoxicity by multiple pathways, [Ca2+]i stabilization may not be the only mechanism responsible for the protective effect of DMF.

PC12 cells transfected with a C-terminal fragment of the amyloid precursor protein (APP C-100), exhibit enhanced sensitivity to the calcium ionophore A23187, and diminished sensitivity to hydrogen peroxide

Extracellular neuritic plaques are a hallmark of Alzheimer's disease. The core protein of plaques is Abeta, a 39-43 amino acid peptide derived from the amyloid precursor protein (APP). APP C-100 is a C-terminal fragment of APP, 100 amino acids long, whose sequence includes Abeta. To determine whether APP C-100 expression alters cellular vulnerability to calcium and H(2)O(2), rat PC12 cells were modified to overexpress APP C-100. Cellular survival (as measured in the MTT assay) was determined as a function of concentration for the calcium ionophore, A23187, and for H(2)O(2) in APP C-100 transfectants and vector-transfected controls. APP C-100 expression significantly increased cellular vulnerability to A23187, and decreased vulnerability to H(2)O(2).

Protective effect of neurotrophic factors, neuropoietic cytokines and dibutyryl cyclic AMP on hydrogen peroxide-induced cytotoxicity on PC12 cells: a possible link with the state of differentiation

We present evidence that the survival of PC12 cells exposed to hydroxyl radicals generated by hydrogen peroxide applied for 30 min at 1 mM was effective when they were differentiated in response to Nerve Growth Factor (NGF) and/or other inducers of neurite outgrowth such as basic-fibroblast growth factor and dibutyryl cyclic AMP. The time- and dose-dependent differentiation triggered by NGF was (1) markedly increased by basic fibroblast growth factor, interleukin-6 or dibutyryl cyclic AMP; (2) diminished by leukemia inhibitory factor or ciliary neurotrophic factor; (3) not potentiated by insulin-like growth factor I or progesterone. The influence of these various factors and agents on PC12 cells was evaluated by the estimation of neurite outgrowth, whereas their possible protective effects were assessed by the measurement of cell survival. Our results would indicate that the factors and agents that induced differentiation were also able to protect the cells against an oxidative stress.

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.

Mechanism of tetrahydroxy-1,4-quinone cytotoxicity: involvement of CA2+ and H2O2 in the impairment of DNA replication and mitochondrial function

In this work we investigated the toxicity of a polyphenolic p-benzoquinone derivative, the tetrahydroxy-1,4-quinone (THQ) toward V79 Chinese hamster fibroblasts and analyzed the role of H2O2 and Ca2+ in that mechanism. The exposure of exponentially growing cultures to THQ, in the presence of 1.0 mM Ca2+, caused a dose-dependent inhibition of cell growth and DNA synthesis. Complete prevention of those effects by catalase indicated that H2O2-induced damages should underlie both toxic processes. Further detection of a rise in the intracellular free Ca2+ concentration ([Ca2+]i) in cells exposed to THQ plus Ca2+, together with the partial protection conferred by the intracellular Ca(2+)-chelator fura-2 against cell growth inhibition, indicated that a disruption of Ca2+ homeostasis is a determinant event in THQ cytotoxicity. Furthermore, the intracellular accumulation of rhodizonic acid (RDZ), the primary oxidative product of THQ, indicated that THQ, or its corresponding semiquinone form, was entering the cells and undergoing further autoxidation to RDZ. It was also evidenced that mitochondria represent an important target in the development of THQ toxicity, as shown by the disruption of the transmembrane electrical potential (delta psi) of isolated rat liver mitochondria, as well as by the Ca(2+)-release by mitochondria of permeabilized V79 cells. We concluded that disruption of Ca2+ homeostasis and generation of H2O2 are critically involved in THQ-induced impairment of DNA replication and mitochondrial functions, leading ultimately to cell growth inhibition.

Two novel antioxidants, U74006F and U78517F, inhibit oxidant-stimulated calcium influx

Incubation of UC11MG human astrocytoma cells with 250 microM hydrogen peroxide (H2O2) plus 50 microM ferrous ammonium sulfate resulted in two temporally distinct increases in intracellular calcium. The first peak, which occurred within 1 min, was due to release from intracellular stores, whereas the second increase was the result of influx of extracellular calcium. Both U74006F and U78517F, two novel antioxidants, specifically inhibited the second, but not the first peak of calcium. The calcium increase was inhibited 70-80% with incubation with either 0.1 microM U78517F or 10 microM U74006F. Treatment with the drugs also protected against oxidant-induced loss in cell viability. In experiments using the membrane potential dye DiBAC4(3), hydrogen peroxide treatment of cells resulted in membrane depolarization. However, at concentrations up to 100 microM, neither of the drugs had any effect on the H2O2-induced depolarization. The drugs also did not affect membrane depolarization resulting from treatment with tetrapropyl ammonium bromide, a potassium channel blocker. These results indicate that U74006F and U78517F act to inhibit injury-induced calcium fluxes, which may contribute to their in vivo efficacy.

DNA strand breakage, cytotoxicity and mutagenicity of hydrogen peroxide treatment at 4 degrees C and 37 degrees C in L5178Y sublines

Cells from the L5178Y murine lymphoma subline LY-R are twofold more resistant to killing by ionizing radiation than the subline LY-S. In contrast, LY-R cells are more sensitive to killing by hydrogen peroxide. Cells of the two sublines in logarithmic growth phase were treated with hydrogen peroxide in phosphate-buffered saline for 1 h at 4 degrees C or 37 degrees C. From the comparison of D(o) values it followed that at 37 degrees C LY-R were 3.6 times more sensitive to the killing effect of H2O2 than LY-S cells; at 4 degrees C they were 11 times more sensitive. Treatment with hydrogen peroxide at 4 degrees C gave a considerable sparing effect, which was substantially greater for the LY-S subline; for LY-S cells D(o) was 5.7 times lower at 37 degrees C than at 4 degrees C, for LY-R cells only 1.9 times. The mutation frequency (HGPRT) in LY-R cells was increased in proportion to H2O2 concentration and was the same at both treatment temperatures. In contrast, mutation frequencies initially increased, then decreased with increasing H2O2 concentration in LY-S cells treated at 4 or 37 degrees C. The concentration at which the decline was initiated was higher at 4 than at 37 degrees C. DNA damage after H2O2 treatment (both temperatures, 5 min) was estimated from the 'comet' assay (single-cell gel electrophoresis). The initial damage, but not the residual damage, differed significantly in LY sublines. A period of slower repair (between 3 and 10 min) was found in LY-R cells.

Oleic acid supplementation reduces oxidant-mediated dysfunction of cultured porcine pulmonary artery endothelial cells

We have previously shown that supplementing cultured porcine pulmonary artery endothelial cells (PAEC) with exogenous oleic acid (18:1 omega 9) alters the fatty acid composition of the cells and reduces oxidant-mediated cytotoxicity. Because the mechanisms by which lipid alterations modulate oxidant susceptibility have not been defined, the ability of 18:1 to reduce hydrogen peroxide (H2O2)-mediated PAEC dysfunction was evaluated. PAEC monolayers on polycarbonate filters were incubated for 3 h in maintenance medium supplemented with either 0.1 mM 18.1 in ethanol vehicle (ETOH) or with an equivalent volume of vehicle alone. Twenty-four hours later monolayers were treated for 30 min with 50 or 100 microM H2O2 in Hanks' balanced salt solution (HBSS) or with HBSS alone (nonoxidant control). As a functional index of PAEC monolayer integrity, the permeability of monolayers to albumin was then measured for 3 h. Treatment with 100 microM H2O2 caused cytotoxicity and progressive increases in PAEC monolayer permeability that were attenuated by 18:1 supplementation, whereas 50 microM H2O2 caused only a transient increase in permeability without cytotoxicity. Supplementation with 18:1 also attenuated H2O2-induced reductions in PAEC adenosine triphosphate (ATP) content and disruption of PAEC microfilament architecture. The ATP content of PAEC monolayers was reversibly reduced in the absence of oxidant stress by incubation with glucose-depleted medium containing deoxyglucose and antimycin A. Metabolic inhibitor-induced ATP depletion increased monolayer permeability and altered cytoskeletal architecture, alterations that resolved during recovery of PAEC ATP content. These results demonstrate that ATP depletion plays a critical role in barrier dysfunction and suggests that the ability of 18:1 to reduce oxidant-mediated PAEC dysfunction and injury may relate directly to its ability to preserve PAEC ATP content.

A cellular model of oxidant-mediated neuronal injury

Oxidants derived from the partial reduction of oxygen are thought to play a significant role in neuronal injury. We present here a cellular model of neuronal injury mediated by hydrogen peroxide (H2O2) using the PC 12 rat pheochromocytoma cell line. The organization of microtubules and microfilaments within neurites of PC 12 cells differentiated by exposure to nerve growth factor was examined after H2O2 injury using fluorescence microscopy. Concentrations of H2O2 as low as 100 microM produced an initial periodic pattern of microtubule depolymerization over 3-4 h which later progressed to complete depolymerization. Neuritic microspikes containing actin filaments were relatively more resistant to injury by H2O2 than microtubules. Blebbing of PC 12 cell bodies and neurites also was seen after H2O2 injury and the blebs appeared to contain microtubules. The destructive changes affecting neuritic structure preceded but were not essential for PC 12 cell lysis. Exposure of the cells to the Ca2+ ionophore, ionomycin (25 microM) also produced the same pattern of microtubule depolymerization in PC 12 neurites as was seen after H2O2 injury suggesting that H2O2 may mediate its destructive effect on the neurites via elevation of intracellular Ca2+.

Killing of endothelial cells and release of arachidonic acid. Synergistic effects among hydrogen peroxide, membrane-damaging agents, cationic substances, and proteinases and their modulation by inhibitors

51Chromium-labeled rat pulmonary artery endothelial cells (EC) cultivated in MEM medium were killed, in a synergistic manner, by mixtures of subtoxic amounts of glucose oxidase-generated H2O2 and subtoxic amounts of the following agents: the cationic substances, nuclear histone, defensins, lysozyme, poly-L-arginine, spermine, pancreatic ribonuclease, polymyxin B, chlorhexidine, cetyltrimethyl ammonium bromide, as well as by the membrane-damaging agents phospholipases A2 (PLA2) and C (PLC), lysolecithin (LL), and by streptolysin S (SLS) of group A streptococci. Cytotoxicity induced by such mixtures was further enhanced by subtoxic amounts either of trypsin or of elastase. Glucose-oxidase cationized by complexing to poly-L-histidine proved an excellent deliverer of membrane-directed H2O2 capable of enhancing EC killing by other agonists. EC treated with rabbit anti-streptococcal IgG were also killed, in a synergistic manner, by H2O2, suggesting the presence in the IgG preparation of cross-reactive antibodies. Killing of EC by the various mixtures of agonists was strongly inhibited by scavengers of hydrogen peroxide (catalase, dimethylthiourea, MnCl2), by soybean trypsin inhibitor, by polyanions, as well as by putative inhibitors of phospholipases. Strong inhibition of cell killing was also observed with tannic acid and by extracts of tea, but less so by serum. On the other hand, neither deferoxamine, HClO, TNF, nor GTP gamma S had any modulating effects on the synergistic cell killing. EC exposed either to 6-deoxyglucose, puromycin, or triflupromazin became highly susceptible to killing by mixtures of hydrogen peroxide with several of the membrane-damaging agents. While maximal synergistic EC killing was achieved by mixtures of H2O2 with either PLA2, PLC, LL, or with SLS, a very substantial release of [3H]arachidonic acid (AA), PGE2, and 6-keto-PGF occurred only if a proteinase was also added to the mixture of agonists. The release of AA from EC was markedly inhibited either by scavengers of H2O2, by proteinase inhibitors, by cationic agents, by HClO, by tannic acid, and by quinacrin. We suggest that cellular injury induced in inflammatory and infectious sites might be the result of synergistic effects among leukocyte-derived oxidants, lysosomal hydrolases, cytotoxic cationic polypeptides, proteinases, and microbial toxins, which might be present in exudates. These "cocktails" not only kill cells, but also solubilize AA and several of its metabolites. However, AA release by the various agonists can be also achieved following attack by leukocyte-derived agonists on dead cells. It is proposed that treatment by "cocktails" of adequate antagonists might be beneficial to protect against cellular injury in vivo.

Disruption of Ca2+ homeostasis in Trypanosoma cruzi by crystal violet

We have demonstrated previously that crystal violet induces a rapid, dose-related collapse of the inner mitochondrial membrane potential of Trypanosoma cruzi epimastigotes. In this work, we show that crystal violet-induced dissipation of the membrane potential was accompanied by an efflux of Ca2+ from the mitochondria. In addition, crystal violet inhibited the ATP-dependent, oligomycin-, and antimycin A-insensitive Ca2+ uptake by digitonin-permeabilized epimastigotes. Crystal violet also induced Ca2+ release from the mitochondria and endoplasmic reticulum of digitonin-permeabilized trypomastigotes. Furthermore, crystal violet inhibited Ca2+ uptake and the (Ca(2+)-Mg2+)-ATPase of a highly enriched plasma membrane fraction of epimastigotes, thus indicating an inhibition of other calcium transport mechanisms of the cells. Disruption of Ca2+ homeostasis by crystal violet may be a key process leading to trypanosome cell injury by this drug.

Sublethal oxidant stress induces a reversible increase in intracellular calcium dependent on NAD(P)H oxidation in rat alveolar macrophages

A concentration-dependent elevation of intracellular calcium ([Ca2+]i) and oxidation of NAD(P)H occurred in alveolar macrophages during exposure to sublethal tert-butylhydroperoxide concentrations (tBOOH) (< or = 100 microM in 1 ml with 1 x 10(6) cells). Oxidation of NAD(P)H preceded a rise in [Ca2+]i. The elevation of [Ca2+]i was reversible at < 50 microM tBOOH exposure and the return to the steady state [Ca2+]i correlated temporally with repletion of NAD(P)H. At > 50 microM tBOOH, the changes in NAD(P)H and [Ca2+]i were sustained. The relative contributions of NADPH and NADH oxidation were examined by varying the substrates supplying reducing equivalents and by inhibiting glutathione reductase activity. The results suggested that at < 50 microM tBOOH, oxidation of NADPH predominated, while at > 50 microM tBOOH, NADH oxidation predominated. A complex relationship between the relative roles of NADPH and NADH oxidation and the elevation of [Ca2+]i was revealed: (i) reversible oxidation of NADPH is associated with the initial and reversible elevation of [Ca2+]i at < 50 microM tBOOH; (ii) the sustained elevation of [Ca2+]i at > 50 microM tBOOH correlates with the sustained oxidation of NADH; and (iii) the changes in [Ca2+]i did not depend on influx of extracellular Ca2+. We speculate that at low tBOOH, Ca2+ was released from the NADPH/NADP(+)-sensitive mitochondrial Ca2+ pool while higher tBOOH caused additional Ca2+ release from GSH/GSSG-sensitive nonmitochondrial Ca2+ pools with sustained elevation of [Ca2+]i due to decreased mitochondrial Ca2+ reuptake.

Nerve growth factor effects on pyridine nucleotides after oxidant injury of rat pheochromocytoma cells

Neurotrophic factors regulate neuronal survival and neurite growth in development and following injury. Oxidative stress produced in neurons as a consequence of primary injury, or during reperfusion following ischemia, may contribute to cell death. Here, the effects of nerve growth factor (NGF) on the response to H2O2 injury were examined in the PC12 rat pheochromocytoma cell line. Specifically, the effect of NGF on cell viability after H2O2 injury was measured. Pretreatment with NGF enhanced survival after H2O2 treatment, as measured by Trypan blue dye exclusion, radiolabeled amino acid incorporation, tetrazolium salt reduction, or cytoplasmic enzyme release. One early event associated with H2O2 treatment was a rapid decrease in NAD+. Although initial decreases in NAD+ levels were similar in control and NGF-treated cells, the latter recovered more rapidly and extensively. The decline in total NAD observed after NGF treatment was almost equal in magnitude to the measured increase in NADP. Inhibition of poly(ADP-ribose) polymerase also enhanced viability following H2O2 injury. Treatment with both NGF and an inhibitor of this enzyme resulted in a greater reduction of H2O2 toxicity than was observed with either agent alone. These data suggest that NGF protection is multifactorial and that a significant component of the NGF effect is due to its regulatory role in the metabolism of pyridine nucleotides.