Effects Of Reactive Oxygen Intermediates Research Articles

Влияние металлов переменной валентности на окислительную модификацию аминокислотных остатков альбумина

BACKGROUND: The constancy of the protein composition of the body is one of the most important conditions for normal vital activity. Deviations in the content of the main bioelements, in particular, mixed valence metals, caused by environmental factors, improper nutrition and other factors, lead to various disorders. One of the properties of metals of mixed valence is the abil-ity to cause metal-catalyzed oxidation of proteins in joint action with active forms of oxygen. It seems interesting to study the oxidative modification of the amino acid residues of albumin and the change in its properties. AIM: To study the effect of reactive oxygen intermediates generated by the Fenton reaction in the presence of Fe2+ and Cu2+ on the oxidative modification of amino acid residues of bovine serum albumin. MATERIALS AND METHODS: The study was carried out on bovine serum albumin (BSA), which was incubated for 2 hours in a mixture of Fenton's reagents – FeSO4 + H2O2 and in a mixture of СuSO4 + H2O2. The quantitative protein content in the samples was determined with the bromcresol green reagent (Albumin-Olvex). The content of carbonyl derivatives of proteins was estimated by the method of R.L. Levine modified by E.E. Dubinina. The content of thiol groups in albumin samples from the control and experimental groups was determined by the Ellman method with DTNB (under non-denaturing conditions. RESULTS: The presented results demonstrate that under the action of Cu2+ ions, the formation of carbonyl derivatives of aliphatic amino acids of albumin is less than in the presence of Fe2+, which can be explained by the different degrees of albumin affinity to metals of variable valence. The rate of mobility of oxidatively modified albumin in polyacrylamide gel decreases, which is explained by protein aggregation due to bityrosine cross-links. CONCLUSION: Variable valence metals affect the modification of albumin. The change in the functional properties of the protein is of physiological significance, including the case of extracellular mobilization of iron and copper.

The effect of reactive oxygen intermediates, exometabolites of organotrophic bacteria, on initiation of zinc corrosion

The effect of reactive oxygen intermediates, such as superoxide radical and hydrogen peroxide, on the initiation of biological zinc corrosion is demonstrated. A correlation between the amounts of formed hydrogen peroxide and the corrosive activity of the studied bacteria is revealed.

The cytoprotective role of the Keap1–Nrf2 pathway

An elaborate network of highly inducible proteins protects aerobic cells against the cumulative damaging effects of reactive oxygen intermediates and toxic electrophiles, which are the major causes of neoplastic and chronic degenerative diseases. These cytoprotective proteins share common transcriptional regulation, through the Keap1-Nrf2 pathway, which can be activated by various exogenous and endogenous small molecules (inducers). Inducers chemically react with critical cysteine residues of the sensor protein Keap1, leading to stabilisation and nuclear translocation of transcription factor Nrf2, and ultimately to coordinate enhanced expression of genes coding for cytoprotective proteins. In addition, inducers inhibit pro-inflammatory responses, and there is a linear correlation spanning more than six orders of magnitude of concentrations between inducer and anti-inflammatory activity. Genetic deletion of transcription factor Nrf2 renders cells and animals much more sensitive to the damaging effects of electrophiles, oxidants and inflammatory agents in comparison with their wild-type counterparts. Conversely, activation of the Keap1-Nrf2 pathway allows survival and adaptation under various conditions of stress and has protective effects in many animal models. Cross-talks with other signalling pathways broadens the role of the Keap1-Nrf2 pathway in determining the fate of the cell, impacting fundamental biological processes such as proliferation, apoptosis, angiogenesis and metastasis.

Coordinate regulation of enzyme markers for inflammation and for protection against oxidants and electrophiles

An elaborate network of highly inducible phase 2 proteins protects aerobic cells against the cumulative damaging effects of reactive oxygen intermediates and toxic electrophiles, which are the major causes of malignancy and chronic degenerative diseases. Many chemical and phytochemical agents, all of which react with thiol groups, induce the phase 2 response through their reactivity with critical cysteine thiols of Keap1. We recently found that the anti-inflammatory potencies (suppression of iNOS and COX-2 expression) of a series of triterpenoids with Michael reaction centers were closely correlated with the potencies of these agents to induce the phase 2 response. We now report that representatives of seven recognized chemical classes of inducers, including isothiocyanates, bisbenzylidenes, arsenicals, heavy metals, and vicinal dithiols, showed highly correlated inducer and anti-inflammatory potencies spanning more than six orders of magnitude of concentrations in established cells and in primary mouse peritoneal macrophages. Potency measurements were expressed as the D(m) values (median effect concentration) by use of the Median Effect Equation. Whereas the phase 2 induction required the functional integrity of both the repressor Keap1 and the transcription factor Nrf2, the effectiveness of inducers in blocking the up-regulation of iNOS by inflammatory cytokines was related to the nature of the cytokine and the inducer concentration. These studies identify suppression of inflammation as a consistent property of inducers of the phase 2 response and strongly suggest that this property is a central aspect of their chemoprotective actions.

Hydrogen Peroxide Reverses IL-5 Afforded Eosinophil Survival and Promotes Constitutive Human Eosinophil Apoptosis

Background: Eosinophils play a central role in the induction and perpetuation of allergic inflammatory responses. The present study was performed to investigate the effects of reactive oxygen intermediates on constitutive apoptosis as well as on interleukin (IL)-5 afforded human eosinophil survival. Methods: Peripheral blood eosinophils were isolated by CD16-negative selection to >99% purity and were cultured for 48 h. The number of apoptotic eosinophils in the culture was assessed by flow cytometric analysis of relative DNA content in propidium-iodide-stained cells, annexin-V binding or by morphological analysis. Apoptosis was confirmed by the appearance of a typical ladder pattern in the DNA fragmentation assay by agarose gel electrophoresis. Results: Exogenous H₂O₂ reversed IL-5-afforded eosinophil survival by inducing apoptosis. Constitutive eosinophil apoptosis was inhibited by a reduction of intracellular levels of H₂O₂ by catalase. Exogenous H₂O₂ increased the rate of constitutive apoptosis. Conclusions: Our results suggest that H₂O₂ may play a role in the downregulation of eosinophilic inflammation by inducing eosinophil apoptosis.

Phytomonas spp: superoxide dismutase in plant trypanosomes

In 1909, Donovan [1] proposed the creation of a new genus, Phytomonas, to differentiate plant from animal trypanosomatids. Phytomonas spp. live in the latex, sap, sieve tubes, and fruit of many plant species [2]. At first, considerable controversy surrounded the pathogenicity of phytomonads in plants, as initially these parasitic protozoans were not thought to be particularly harmful. However, evidence from a number of plants of great economic significance, such as coffee, coconut, and palm, has shown that Phytomonas infections can have devastating economic consequences [3]. The defence mechanisms of trypanosomatids against the toxic products of O2 reduction – e.g. superoxide anion, hydrogen peroxide or hydroxyl radicals – are not completely understood. Trypanosomatids are protected from the damaging effects of reactive oxygen intermediates by scavengers such as trypanothione and specific enzymes such as superoxide dismutase (SOD, EC 1.15.1.1) and trypanothione peroxidase. Catalase, involved in the elimination of hydrogen peroxide, is absent from most trypanosomatids, although it has been detected in Crithidia luciliae [4] and in Phytomonas spp. [5]. Cyanide-insensitive SOD activity has been reported in Trypanosoma cruzi [6], as well as in other trypanosomatids such as Crithidia fasciculata [7] and Trypanosoma brucei [4]. The SOD activities of Leishmania tropica and T. cruzi are also cyanide-insensitive but peroxide-sensitive [7]. SOD of C. fasciculata is located in the cytosol and exists in three forms, which may represent three distinct isozymes. Comparisons of the amino-acid sequence of this SOD with those of SODs from other sources suggest that the crithidial enzyme is closely related to bacterial FeSOD of the alga Euglena gracilis. SOD activity has also been detected in L. dono ani and Phytomonas spp., although its nature has not been determined [8,9]. Most of the information on the biochemistry of plant flagellates has come from experiments in which the flagellates were used as instruments in biochemical research rather than from studies investigating the biochemistry of the plant flagellates themselves. Probably for this reason, these studies are scattered through a variety of subjects, and, despite the amount of information gathered in recent years, our knowledge of the biochemistry of Phytomonas remains fragmentary [3]. In this sense, the detoxifying mechanisms of oxygen radicals in plant trypanosomatids are unknown. From previous studies [10], we know that plant flagellates have SOD activity, but we have yet to identify the role of this enzyme in the destruction of the superoxide radicals, and there is no information available on the enzyme itself. In the present work, we confirm and quantify the SOD activity in three trypanosomes isolated from different plants: from phloem of the Coco nucifera (Hartrot disease) [11], from latex vessels of Euphorbia characias [12], from the fruits of Lycopersicon esculenAbbre iations: Cu/ZnSOD, copper/zinc-containing superoxide dismutase; FeSOD, iron-containing superoxide dismutase; ME, malic enzyme; MnSOD, manganese-containing superoxide dismutase; NBT, nitro-blue tetrazolium salt; PK, pyruvate kinase; PFK, 6-phospho fructose kinase; SOD, superoxide dismutase. * Corresponding author. Tel.: +34-958-242369; fax: +34-958243174. E-mail address: msanchem@goliat.ugr.es (M. Sanchez-Moreno).

Inhibition by singlet molecular oxygen of the vascular reactivity in rabbit mesenteric artery.

1. The effects of reactive oxygen intermediates derived from photoactivated rose bengal on the vascular reactivity have been evaluated in rabbit mesenteric artery ring preparations. The artery rings were exposed to xanthene dye rose bengal (50 nM) illuminated (6,000 lux) at 560 nm for 30 min. Spin trapping studies with 2,2,6,6-tetramethylpiperidine (TEMP) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) with electron spin resonance spectrometry were also conducted in solution (and not within tissues) to determine quantitatively the reactive oxygen species generated from photoactivated rose bengal. 2. Contraction of the ring preparations induced by noradrenaline (10(-8) to 10(-4) M) was attenuated by previous exposure to photolysed rose bengal; the observation that the pD2 decreased without a significant reduction in maximum tension generation is consistent with the view that receptor dysfunction may be involved in the effect of photolysed rose bengal. 3. Prior exposure to photolysed rose bengal of the ring preparations inhibited the endothelium-dependent relaxation evoked by acetylcholine (10(-6) M) and calcium ionophore A23187 (10(-7) M), but not the endothelium-independent relaxation evoked by nitroglycerin (10(-6) M). 4. A variety of scavengers, superoxide dismutase (33 units ml-1), catalase (32 units ml-1) and 1,3-dimethyl-2-thiourea (DMTU, 10 mM), which should eliminate the superoxide anion radical, H2O2 and the hydroxyl radical, had no effect on the attenuated responses to noradrenaline and acetylcholine induced by photolysed rose bengal. In contrast, the inhibition of the observed effect of photolysed rose bengal was obtained with addition of histidine (25 mM), a singlet molecular oxygen quencher. 5. It was found that photolysis of rose bengal from a 1:2:2:1 quartet, characteristic of the hydroxyl radical-DMPO spin adduct, which was effectively blunted by DMTU, superoxide dismutase and catalase whereas histidine was ineffective. The results of the electron spin resonance study also showed that a singlet molecular oxygen was produced by photoactivation of rose bengal; this was detected as singlet oxygen-TEMP product (TEMPO; 2,2,6,6-tetramethylpiperidine-N-oxyl). The formation of the TEMPO signal was strongly inhibited by histidine, but not by DMTU, superoxide dismutase and catalase. 6. It is suggested that the superoxide anion radical, H2O2 and hydroxyl radical are formed in addition to singlet molecular oxygen, and the data obtained from the present study indicate that singlet molecular oxygen is one of the most destructive oxygen species. Endothelium-dependent relaxation is quite vulnerable to singlet molecular oxygen. Singlet oxygen also depresses noradrenaline-induced contraction possibly via alpha-adrenoceptor dysfunction. This, in turn, may lead to vascular incompetence.

Susceptibility of caffeine- and Ins(1,4,5)P 3-induced contractions to oxidants in permeabilized vascular smooth muscle

Two principal pathways of Ca 2+ release from the sarcoplasmic reticulum of excitable and non-excitable cells have been described: one pathway dependent on the second messenger d- myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P 3), and a second pathway sensitive to Ca 2+ and regulated by caffeine and ryanodine. It was found that the Ca 2+-pump activity of vascular smooth muscle sarcoplasmic reticulum is inhibited by superoxide anion radicals (O 2 ⋅−); however, the effects of reactive oxygen intermediates on sarcoplasmic reticulum Ca 2+ release in vascular muscle cells are not well defined. The purpose of the present study was to evaluate the effects of reactive oxygen intermediates generated from the hypoxanthine/xanthine oxidase reaction system on contractions induced by caffeine, Ins(1,4,5)P 3 and norepinephrine in staphylococcal α-toxin-permeabilized rabbit mesenteric arteries. This system generates O 2 ⋅−, H 2O 2, and hydroxyl radicals. We wished to identify which class of reactive oxygen intermediates is responsible for the associated loss of vascular smooth muscle contractile function. Caffeine and Ins(1,4,5)P 3 produced a transient contraction when the sarcoplasmic reticulum of the permeabilized preparations was preloaded with pCa 7.0 solution for 5 min before washing with 0.5 mM EGTA solution; norepinephrine also produced a transient contraction. Exposure of the preparations to hypoxanthine/xanthine oxidase (for 30 min) attenuated caffeine-induced contraction, but was without effect on Ins(1,4,5)P 3-induced contraction. The observed effect of hypoxanthine/xanthine oxidase exposure was superoxide dismutase-inhibitable, suggesting O 2 ⋅− involvement. Hypoxanthine/xanthine oxidase also inhibited norepinephrine-induced contraction. The effect of hypoxanthine/xanthine oxidase on norepinephrine contraction was protected by catalase, but not by superoxide dismutase and dimethyl sulfoxide; exogenously added H 2O 2 mimicked the effect of hypoxanthine/xanthine oxidase exposure. H 2O 2, added exogenously, was without effect on Ins(1,4,5)P 3-induced contraction. It is suggested that the pathway of Ca 2+ release from the sarcoplasmic reticulum dependent on Ins(1,4,5)P 3 is insensitive to O 2 ⋅−. Instead, caffeine-induced Ca 2+ release mechanisms may be susceptible to O 2 ⋅− and H 2O 2, rather than O 2 ⋅− and hydroxyl radicals, may be the active agent in the norepinephrine-induced contraction. Our results are also consistent with the view that the attenuation by H 2O 2 of the norepinephrine-induced contraction may be linked to the receptor-associated pathway of Ins(1,4,5)P 3 formation, but not to degradation processes of Ins(1,4,5)P 3.

Transcriptional regulation of Schistosoma mansoni calreticulin: possible role of AP-1.

Little is known about the regulation and control of Schistosoma mansoni gene expression. In order to study such mechanisms a gene reporter expression vector construction, under the control of a promoter region derived from the S. mansoni calreticulin gene was used to transfect the human Jurkat T cell line. The promoter region contains potential TATA and CAAT boxes as well as an AP-1 core element. We show here that transcriptional factors of eucaryotic cells may induce a gene reporter activity under the control of a S. mansoni promoter region. Treatment of stably transfected cells with N-acetyl cysteine (NAC), a well-characterized antioxidant which counteracts the effects of reactive oxygen intermediates, enhanced the AP-1 dependent transactivation. This effect was abolished when the SmCaR promoter region was deleted in the AP-1 site. Electrophoretic Mobility Shift Assays showed that the AP-1 sequence of S. mansoni bound to both S. mansoni extracts and in nuclear extracts from Jurkat cells, thus explaining possible activation of AP-1 by NAC. Finally treatment of S. mansoni schistosomula and adult worms with NAC induced an increased synthesis of calreticulin protein suggesting a possible role of redox mechanisms in the regulation of a calreticulin gene transcription process in S. mansoni.

Reactive Oxygen Intermediates Induce Regulated Secretion of von Willebrand Factor From Cultured Human Vascular Endothelial Cells

Exocytosis from Weibel-Palade bodies, the secretory granules of vascular endothelial cells, causes the rapid release of von Willebrand factor (vWF), an adhesive glycoprotein involved in primary hemostasis, and cell surface expression of P-selectin, a membrane protein involved in neutrophil binding. Thus, exocytosis may represent a link between hemostasis and inflammation. We investigated the effect of reactive oxygen intermediates (ROIs) on vWF secretion. Incubation of cultured endothelial cells with xanthine oxidase (XO), which generates superoxide anions (O2-), induces a potent, rapid secretory response. However, vWF release was not observed in response to H2O2. Extracellular, subendothelial vWF deposits typically seen after exocytosis from Weibel-Palade bodies were observed after exposure to XO. XO caused a rapid, sustained increase in intracellular free calcium concentration ([Ca2+]i). vWF secretion was markedly inhibited by BAPTA-AM, a cell-permeant calcium chelator. Removal of extracellular calcium did not inhibit vWF release, although the sustained phase of the [Ca2+]i increase was suppressed. These results suggest that XO-induced vWF release is mediated by the initial increase in [Ca2+]i which is caused by calcium mobilization from intracellular stores rather than by calcium influx. Exocytosis from Weibel-Palade bodies may contribute to the pathogenic effect of ROIs in atherosclerosis and inflammation.

Constitutive expression of human hsp27, Drosophila hsp27, or human alpha B-crystallin confers resistance to TNF- and oxidative stress-induced cytotoxicity in stably transfected murine L929 fibroblasts.

Hyperthermia and other forms of stress that induce and/or stimulate heat shock or stress protein (hsp) expression enhance the cellular resistance to TNF-alpha. One of the stress proteins, hsp70, has been shown to participate in the molecular mechanisms that regulate this phenomenon. Here we have tested the capability of small hsps from different species to protect against this cytokine in the TNF-sensitive L929 fibrosarcoma cells. The genes that encode human hsp27, Drosophila hsp27, and human alpha B-crystallin were placed under the control of the constitutive SV40 early promoter and were stably introduced into L929 cells. We observed that all clones that constitutively expressed the exogenous small hsps exhibited a strong protection against TNF-mediated killing, which was proportional to the level of the expressed proteins. This phenomenon did not correlate with altered binding of TNF-alpha to its receptors, and no protection was observed as a consequence of the transfection or selection procedures. In addition, the overexpression of the exogenous small hsps did not modify the level of the endogenous stress proteins in the transfected clones. Remarkably, the small hsps also induced a protection against oxidative stresses generated by either hydrogen peroxide or menadione. In L929 cells, the killing induced by TNF-alpha and oxidative stress is thought to occur through the accumulation of intracellular reactive oxygen intermediates. Hence, our data suggest that the small hsps from different species share the property to protect L929 cells against the deleterious effects of reactive oxygen intermediates generated by either TNF-alpha or oxidative stress.

Effect of reactive oxygen intermediates on the in vitro invasive capacity of tumor cells and liver metastasis in mice

We studied the role of reactive oxygen intermediates (ROIs) in experimental liver metastasis induced in mice by the inoculation of COLON 26-M5 murine colon cancer cells, a highly metastatic variant of COLON 26 cells, and the effect of ROIs on the invasive capacity of the cells in an in vitro chemo-invasion assay model using reconstituted basement membrane matrigel. We also measured the release of ROIs from cells using electron spin resonance (ESR) spectrometry. Hydroxyl radicals (.OH) were constitutively released from the cells. This release was augmented by pre-treatment with phorbol 12-myristate 13-acetate (PMA). In experimental liver metastasis in CDF1 mice, the administration of recombinant human superoxide dismutase (r-hSOD) significantly increased the number of metastatic nodules, while administration of catalase significantly inhibited metastasis formation. In vitro pre-treatment of cells with PMA significantly increased the number of metastatic nodules. Invasive capacity of the cells was markedly augmented by pre-treatment with PMA. PMA-induced augmentation was significantly inhibited by the simultaneous addition of r-hSOD to the assay. Catalase had no significant effect. Our findings suggest that ROIs play an important role in tumor invasion and metastasis, and that hydrogen peroxide (H2O2) may contribute to the retention or extravasation of circulating tumor cells. Furthermore, the superoxide anion (O2-) released by tumor cells may play an important role in basement membrane degradation.

Reactive oxygen in skeletal muscle. I. Intracellular oxidant kinetics and fatigue in vitro.

We hypothesized that muscle fiber bundles produce reactive oxygen intermediates and that reactive oxidant species contribute to muscular fatigue in vitro. Fiber bundles from rat diaphragm were mounted in chambers containing Krebs-Ringer solution. In studies of intracellular oxidant kinetics, bundles were loaded with 2',7'-dichlorofluorescin, a fluorochrome that emits at 520 nm when oxidized; emissions were quantified using a fluorescence microscope. Emissions from unstimulated muscles increased over time (P < 0.001). Accumulation of fluorescence was slowed by addition of catalase (P < 0.001) or superoxide dismutase (P < 0.001) and was accelerated by repetitive muscular contraction (P < 0.05). To determine effects of reactive oxygen intermediates on fatigue, curarized bundles were stimulated to contract isometrically; force was measured. Catalase, superoxide dismutase, and dimethyl sulfoxide were screened for effects on low- and high-frequency fatigue. Antioxidants inhibited low-frequency fatigue [after 5 min of repetitive contractions, force at 30 Hz was 20% greater than control (P < 0.015)] and increased the variability of fatigue at 30 Hz (P < 0.03). Antioxidants did not alter high-frequency (200-Hz) fatigue. We conclude that 1) diaphragm fiber bundles produce reactive oxygen intermediates, including O2-. and H2O2; 2) muscular contraction increases intracellular oxidant levels; and 3) reactive oxygen intermediates promote low-frequency fatigue in this preparation.

Neurovascular effects of reactive oxygen intermediates produced by photoradiation

These experiments examined the effect of reactive oxygen intermediates, produced by laser illumination of the photosensitizer hematoporphyrin derivative, on the accumulation and release of norepinephrine from sympathetic nerve terminals. Using an isolated, spirally cut, superfused caudal artery of the rat, basal overflow of norepinephrine (NE) was significantly increased both during and after generation of reactive oxygen intermediates. Generation of reactive oxygen intermediates increased overflow of NE in vascular preparations in which release of NE had previously been elevated by the continuous superfusion of Krebs' solution, containing high concentrations of potassium (40 mM). Calcium free solutions did not block the overflow of norepinephrine augmented by reactive oxygen intermediates. This increase in overflow was due both to an increase in release of NE and an inhibition of accumulation of NE.

Reactive oxygen intermediates as apparently widely used messengers in the activation of the NF-kappa B transcription factor and HIV-1.

Hydrogen peroxide and oxygen radicals are agents commonly produced during inflammatory processes. In this study, we show that micromolar concentrations of H2O2 can induce the expression and replication of HIV-1 in a human T cell line. The effect is mediated by the NF-kappa B transcription factor which is potently and rapidly activated by an H2O2 treatment of cells from its inactive cytoplasmic form. N-acetyl-L-cysteine (NAC), a well characterized antioxidant which counteracts the effects of reactive oxygen intermediates (ROI) in living cells, prevented the activation of NF-kappa B by H2O2. NAC and other thiol compounds also blocked the activation of NF-kappa B by cycloheximide, double-stranded RNA, calcium ionophore, TNF-alpha, active phorbol ester, interleukin-1, lipopolysaccharide and lectin. This suggests that diverse agents thought to activate NF-kappa B by distinct intracellular pathways might all act through a common mechanism involving the synthesis of ROI. ROI appear to serve as messengers mediating directly or indirectly the release of the inhibitory subunit I kappa B from NF-kappa B.

Inhibition of Ca(2+)-ATPase of vascular smooth muscle sarcoplasmic reticulum by reactive oxygen intermediates

Effects of reactive oxygen intermediates generated by hypoxanthine plus xanthine oxidase on the Ca(2+)-adenosinetriphosphatase (ATPase) of sarcoplasmic reticulum from bovine aortic smooth muscle were studied. Exogenous hypoxanthine (0.1-100 microM) plus xanthine oxidase (10 mU/ml) produced an hypoxanthine concentration-dependent inhibition of the Ca(2+)-ATPase. The inhibition could be completely blocked by superoxide dismutase (100 U/ml) but not by either mannitol (20 mM) or deferoxamine (100 microM). Direct addition of hydrogen peroxide in the micromolar range did not cause significant inhibition. These results suggest that superoxide is the primary damaging species. Cysteine blocked this inhibition, suggesting possible involvement of sulfhydryl groups in the inhibition mechanism. Additionally, 1.16 +/- 0.17 mU/g wet wt of xanthine oxidase activity was detected in the postnuclear supernatant of bovine aortic smooth muscle, suggesting the existence of a possible intracellular source of superoxide. This value was calculated to be approximately 5 mU/ml by using a usual value of vascular smooth muscle cellular volume. Thus the level of endogenous xanthine oxidase in vascular smooth muscle is comparable with the level of exogenous xanthine oxidase used in the present study. These findings suggest a potential role of xanthine oxidase-generated superoxide in oxidative damage to vascular smooth muscle during a number of pathophysiological conditions.

Functional and electrophysiological effects of reactive oxygen intermediates on isolated rat ventricular muscle: Hiroshi Matsuura and Michael J. Shattock. Cardiovascular Research, The Rayne Institute, St. Thomas' Hospital, London SE1 7EH

Functional and electrophysiological effects of reactive oxygen intermediates on isolated rat ventricular muscle: Hiroshi Matsuura and Michael J. Shattock. Cardiovascular Research, The Rayne Institute, St. Thomas' Hospital, London SE1 7EH

Selective modification of glutathione metabolism.

Glutathione, a tripeptide thiol found in virtually all cells, functions in metabolism, transport, and cellular protection. It participates in the reduction of disulfides and other molecules, and conjugates with compounds of exogenous and endogenous origin. It protects cells against the destructive effects of reactive oxygen intermediates and free radicals. Modifications of glutathione metabolism may be achieved by administration of selective enzyme inhibitors, and also by giving compounds that increase glutathione synthesis. Such effects are useful in chemotherapy and radiation therapy and in protecting cells against the toxic effects of drugs, other foreign compounds, and oxygen.