Hydroxyl-radical-induced iron-catalysed degradation of 2-deoxyribose. Quantitative determination of malondialdehyde

The degradation of 2-deoxyribose to thiobarbituric acid-reactive material was investigated with two hydroxyl-radical-generating systems: (i) a defined gamma-radiolysis method and (ii) incubation with FeSO4 in phosphate buffer. In each case the thiobarbituric acid-reactive material can be accounted for by malondialdehyde, as measured by an h.p.l.c. method for free malondialdehyde. In the radiolysis system there is a large post-irradiation increase in free malondialdehyde if iron ions are added to the samples. It is proposed that this is due to iron ions catalysing the formation of hydroxyl radicals from radiolytically generated H2O2 as well as stimulating the breakdown of an intermediate deoxyribose degradation product. A mechanism for the formation of malondialdehyde during deoxyribose degradation is proposed.

Inhibition of influenza virus replication in tissue culture by 2-deoxy-2,3-dehydro-N-trifluoroacetylneuraminic acid (FANA): mechanism of action

The neuraminidase inhibitor 2-deoxy-2,3-dehydro-N-trifluoroacetylneuraminic acid (FANA) inhibits the mutlicycle replication of influenza viruses in tissue culture. Influenza virus grown in the presence of FANA contains neuraminic acid on its envelope which then serves as receptor for other virus particles causing extensive aggregation. Thus, FANA inhibits influenza virus replication by preventing the enzymatic removal of neuraminic acid from the virus envelope.

Nano-photosensitizer based on layered double hydroxide and isophthalic acid for singlet oxygenation and photodynamic therapy

Singlet oxygen has won a great deal of attention to catalysis and biological studies due to its strong oxidizing properties. However, the photosensitizers which require for the generation of singlet oxygen remain inadequate because of their lack of long-wavelength absorption, weak hydrophilicity, and poor biocompatibility. Here, we develop near-infrared laser activated supramolecular photosensitizers (isophthalic acid/layered double hydroxide nanohybrids) for efficient two-photon photodynamic therapy. The singlet oxygen quantum yield of nanohybrid is up to 0.74. Critically, in vitro tests verify the superior anti-cancer properties of nanohybrid with an IC50 determine to be 0.153 μg mL-1. The nanohybrids take advantage of the superior tissue penetration of 808 nm laser irradiation and exhibit a dramatically strong ability to ablate tumors in vivo, with extremely low toxicity. This work provides the proof of concept that ultralong-lived triplet excitons can function as two-photon-activated photosensitizers for an effective singlet oxygen generation.

Bacterial adaptation to oxidative stress: implications for pathogenesis and interaction with phagocytic cells

During phagocytosis, phagocytic cells generate superoxide and other reactive oxygen species, which are involved in antibacterial activity. However, many bacteria possess antioxidant defenses that may explain their survival in inflammatory foci. These defenses include antioxidant enzymes such as superoxide dismutase and catalase, DNA repair systems, scavenging substrates, and competition with phagocytes for molecular oxygen. These defenses are probably coordinated, and different responses occur with different reactive oxygen species. Escherichia coli and Salmonella typhimurium mutants have allowed the demonstration of a variety of critical genes for enzymatic defense and DNA repair, as well as an oxyR regulon system. In more complex systems, the conditions found in inflammatory foci, such as decreasing glucose and the production of lactate, enhance bacterial catalase production and resistance to hydrogen peroxide. Resistance and adaptation to phagocyte-derived oxidant stress are critical aspects of bacterial pathogenesis.

Stabilization and preservation of Lactobacillus acidophilus in saccharide matrices

Lyophilization and vacuum- or spray-drying are some of the most useful techniques for preserving foods, agricultural products, and pharmaceuticals. Biological materials, however, can be irreversibly damaged during these treatments. Therefore, it is essential to design protective agents to preserve protein activity and cell viability. In this paper we examine the use of alpha, alpha-trehalose-borate systems as protectants for Lactobacillus acidophilus during freeze- and vacuum-drying. Trehalose was found to be an effective protectant for freeze-dried and vacuum-dried samples, and it is equivalent to a protective formulation which is in current industrial use. It is known from our previous work on enzymes that the presence of borate can dramatically enhance the protective ability of trehalose. In this work, the addition of trehalose-borate to bacterial concentrate greatly improves the recovery of viable cells after storage. This improvement was seen in freeze-dried samples stored at 37 degrees C as well as for vacuum-dried samples held at room temperature. A tailored buffering strategy was tested to counteract the high pH resulting from the addition of borate to the mixture. Use of citric or lactic acids in combination with ammonium hydroxide gave a protectant solution with high pH (resulting in effective crosslinking between trehalose and borate) but a dry product with reduced pH upon rehydration (conducive to cell survival). These results raise exciting possibilities for protection of more labile prokaryotic species as well as simple eukaryotes.

OSM1/SYP61: a syntaxin protein in Arabidopsis controls abscisic acid-mediated and non-abscisic acid-mediated responses to abiotic stress

To identify the genetic loci that control salt tolerance in higher plants, a large-scale screen was conducted with a bialaphos marker-based T-DNA insertional collection of Arabidopsis ecotype C24 mutants. One line, osm1 (for osmotic stress-sensitive mutant), exhibited increased sensitivity to both ionic (NaCl) and nonionic (mannitol) osmotic stress in a root-bending assay. The osm1 mutant displayed a more branched root pattern with or without stress and was hypersensitive to inhibition by Na(+), K(+), and Li(+) but not Cs(+). Plants of the osm1 mutant also were more prone to wilting when grown with limited soil moisture compared with wild-type plants. The stomata of osm1 plants were insensitive to both ABA-induced closing and inhibition of opening compared with wild-type plants. The T-DNA insertion appeared in the first exon of an open reading frame on chromosome 1 (F3M18.7, which is the same as AtSYP61). This insertion mutation cosegregated closely with the osm1 phenotype and was the only functional T-DNA in the mutant genome. Expression of the OSM1 gene was disrupted in mutant plants, and abnormal transcripts accumulated. Gene complementation with the native gene from the wild-type genome completely restored the mutant phenotype to the wild type. Analysis of the deduced amino acid sequence of the affected gene revealed that OSM1 is related most closely to mammalian syntaxins 6 and 10, which are members of the SNARE superfamily of proteins required for vesicular/target membrane fusions. Expression of the OSM1 promoter::beta-glucuronidase gene in transformants indicated that OSM1 is expressed in all tissues except hypocotyls and young leaves and is hyperexpressed in epidermal guard cells. Together, our results demonstrate important roles of OSM1/SYP61 in osmotic stress tolerance and in the ABA regulation of stomatal responses.

Rapid method that aids in distinguishing Gram-positive from Gram-negative anaerobic bacteria

Several species of anaerobic bacteria display variable Gram stain reactions which often make identification difficult. A simple, rapid method utilizing a 3% solution of potassium hydroxide to distinguish between gram-positive and gram-negative bacterial was tested on 213 strains of anaerobic bacteria representing 19 genera. The Gram stain reaction and KOH test results were compared with the antibiotic disk susceptibilities (vancomycin and colistin) the preliminary grouping of anaerobic bacteria. All three procedures were in agreement for the majority of strains examined. Some strains of clostridia, eubacteria, and bifidobacteria stained gram negative or gram variable; the KOH and antibiotic disk susceptibility tests correctly classified these strains as gram-positive. The KOH test incorrectly grouped some strains of Bacteroides sp., Fusobacterium sp., Leptotrichia buccalis, and Veillonella parvula, but all Gram stain results for these strains were consistent for gram-negative bacteria. The KOH test is a useful supplement to the Gram stain and antibiotic disk susceptibility testing for the initial classification of anaerobic bacteria.

Protection of mammalian cells by o-phenanthroline from lethal and DNA-damaging effects produced by active oxygen species

Active oxygen species are suspected as being a cause of the cellular damage that occurs at the site of inflammation. Phagocytic cells accumulate at these sites and produce superoxide ion, hydrogen peroxide and hydroxyl radical. The ultimate killing species, the cellular target and the mechanism whereby the lethal injury is produced are unknown. We exposed mouse fibroblasts to xanthine oxidase and acetaldehyde, a system which mimics the membrane of phagocytic cells in terms of production of oxygen species. We observed that the generation of these species produced DNA strand breaks and cellular death. The metal chelator o-phenanthroline completely abolished the former effect, and at the same time it effectively protected the cells from lethal injuries. Because complexing iron o-phenanthroline prevents the formation of hydroxyl radical by the Fendon reaction (Fe(II) + H2O2----Fe(III) + OH- + OH.), it is proposed that most of the cell death and DNA damage are brought about by OH radical, produced from other species by iron-mediated reactions.

Damage to the bases in DNA induced by stimulated human neutrophils

Leukocyte-induced DNA damage may partially account for the known association between chronic inflammation and malignancy. Since elucidation of the chemical nature of leukocyte-induced DNA damage may enhance our understanding of the mechanisms underlying leukocyte-induced DNA damage and the carcinogenesis associated with inflammation, the present study was undertaken to characterize the chemical modifications that occur in DNA exposed to stimulated human neutrophils. Calf thymus DNA was exposed to phorbol myristate acetate (PMA)-stimulated neutrophils in the presence or absence of exogenously added iron ions. DNA samples were subsequently hydrolyzed, derivatized and analyzed by gas chromatography-mass spectrometry with selected-ion monitoring. A variety of base modifications including cytosine glycol, thymine glycol, 4,6-diamino-5-formamidopyrimidine, 8-hydroxyadenine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine, and 8-hydroxyguanine were identified. The yield of these various base products was increased by the addition of iron ions. Specifically, in the presence of physiologic quantities of iron ions, approximately 7 of every 1,000 DNA bases were modified. Addition of the superoxide anion scavenger, superoxide dismutase, the hydrogen peroxide scavenger, catalase, the hydroxyl scavenger, dimethylsulfoxide, or the iron chelator, deferoxamine, to DNA mixtures containing PMA, neutrophils, and iron ions, greatly decreased the yield of the damaged DNA base products. Our results indicate that stimulated human neutrophils can damage each of the four bases in DNA. It is likely that hydroxyl radical, generated via an iron catalyzed Haber-Weiss reaction, mediates neutrophil-induced DNA base damage, since: (a) the chemical structure of neutrophil-induced DNA base damage is consistent with a hydroxyl radical-mediated mechanism, (b) hydroxyl radical generated via ionizing radiation in aqueous solution produces DNA base modifications that are identical to neutrophil-induced DNA base modifications, (c) iron ions increase neutrophil-induced DNA base damage, and (d) iron chelators or scavengers of superoxide anion, hydrogen peroxide or hydroxyl radical decrease neutrophil-induced DNA base damage.

Copper-catalyzed DNA damage by ascorbate and hydrogen peroxide: kinetics and yield

Time profiles for degradation of DNA via reaction of H2O2 with the DNA-Cu+ complex were analyzed over a wide range of concentrations of the components. The yield of DNA damage per H2O2 molecule is 10 times lower than that obtained with gamma-radiolytically generated .OH radicals. The observations can be explained by a model in which H2O2 reacts, slowly on the one hand with DNA-Cu+ by formation of toxic .OH radicals immediately at the DNA and faster on the other hand with Cu+ in the bulk solution by formation of less toxic Cu(III) intermediates.

Hydrogen peroxide: an endogenous smooth muscle cell hyperpolarizing factor

Hydrogen peroxide can be released by different cells such as the nerves, the endothelial or phagocytotic white blood cells which can all interact with vascular smooth muscles. We show that hydrogen peroxide hyperpolarizes and relaxes pig coronary artery smooth muscle cells. The possibility that the endothelium derived hyperpolarizing factor released by the endothelium in response to bradykinin and substance P being hydrogen peroxide was tested using catalase, an enzyme which hydrolyses hydrogen peroxide. We find that this particular endothelial hyperpolarizing factor and hydrogen peroxide are two distinct molecules.

Hydroxyl radical-dependent inactivation of guanylate cyclase in cerebral arterioles by methylene blue and by LY83583

BACKGROUND AND PURPOSE

Methylene blue and 6-anilino,5,8-quinolinedione (LY83583) are used extensively to block activation of guanylate cyclase. Both agents generate oxygen radicals. Therefore, it appeared profitable to investigate whether the generation of oxygen radicals by these agents is responsible for the blockade of responses to nitrodilators that act via activation of guanylate cyclase to relax vascular smooth muscle and cause vasodilation.

METHODS

We tested in anesthetized cats equipped with cranial windows responses to topical application of nitroglycerin, nitroprusside, and adenosine before and during topical application of methylene blue (5 microM). Responses to the vasoactive agents were tested during application of methylene blue after permeabilization of the cell membrane with a detergent to allow methylene blue to enter vascular smooth muscle. Responses were also tested in the presence of superoxide dismutase, catalase, deferoxamine, or dimethyl sulfoxide to scavenge reactive products of oxygen metabolism or to eliminate catalytic iron. In additional experiments we tested the effects of topical application of nitroprusside or adenosine before and after application of LY83583. The responses to the vasoactive agents were also tested in the presence of superoxide dismutase, catalase, or dimethyl sulfoxide in addition to LY83583. We also tested responses to calcitonin gene-related peptide before and in the presence of LY83583 with or without superoxide dismutase.

RESULTS

Methylene blue eliminated the arteriolar dilation in response to nitroprusside and nitroglycerin after permeabilization of the cell membrane with a detergent but not before. The responses to adenosine were unaffected. The blockade induced by methylene blue was reversed by superoxide dismutase, catalase, or dimethyl sulfoxide but not by deferoxamine. LY83583 blocked responses to nitroprusside but not to adenosine. The blockade was eliminated by superoxide dismutase, catalase, or dimethyl sulfoxide. LY83583 blocked the vasodilation induced by calcitonin gene-related peptide. This blockade was reversed by superoxide dismutase.

CONCLUSIONS

Methylene blue and LY83583 prevent the activation of soluble guanylate cyclase by nitrodilators or by calcitonin gene-related peptide by generating oxygen radicals. The mediator of this response is the hydroxyl radical. Methylene blue does not enter the vascular smooth muscle of cerebral arterioles unless the cell membrane is permeabilized.

Selective degeneration of oligodendrocytes mediated by reactive oxygen species

The mechanism underlying demyelination in inflammatory canine distemper encephalitis is uncertain. Macrophages and their secretory products are thought to play an important effector role in this lesion. Recently, we have shown that anti-canine distemper virus antibodies, known to occur in chronic inflammatory lesions, stimulate macrophages leading to the secretion of reactive oxygen species (ROS). To investigate whether ROS could be involved in demyelination, dog glial cell cultures were exposed to xanthine/xanthine oxidase (X/XO), a system capable of generating O2-. This treatment resulted in a specific time-dependent degeneration and loss of oligodendrocytes, the myelin producing cells of the central nervous system. Initial degeneration was not associated with a decrease in viability of oligodendrocytes as judged by trypan blue and propidium iodide exclusion. Astrocytes and brain macrophages were not affected morphologically by this treatment. Further, an evaluation of the effect of several ROS scavengers, transition metal chelators and inhibitors of poly (ADP-ribose) polymerase suggests that a metal dependent formation of .OH or a similar highly oxidizing species could be responsible for the observed selective damage to oligodendrocytes.

A novel mechanism for oxidative cleavage of prolyl peptides induced by the hydroxyl radical

Mechanism for the oxidative cleavage of proline-containing peptides induced by the hydroxyl radical (.OH) has been studied. Accompanying the oxidation of prolyl peptides, we discovered the formation of significant amounts of gamma-aminobutyric acid (GABA) in the acid hydrolysates of the oxidized peptides. GABA was assumed to be derived from the 2-pyrrolidone compound and, in addition, its generation led to the assumption that prolyl peptides were mainly cleaved at the proline residues by .OH, accompanied by the oxidative modification of proline by itself. Hence, in order to confirm this prediction, we undertook the reaction of proline with .OH using proline analogue (Z-proline) and isolated the 2-pyrrolidone compound as the major product. We proposed a novel mechanism for formation of the 2-pyrrolidone compound induced by .OH, which has been established for the first time in the oxidative cleavage of prolyl peptides.

Changes in the structure of xyloglucan during cell elongation

Xyloglucans were isolated by sequential extraction of the cell walls of pea (Pisum sativum L. cv. Alaska) with a xyloglucan-specific endoglucanase and KOH. The xyloglucan content and xyloglucan-oligosaccharide composition were determined for fractions obtained from the elongating and non-elongating segments of pea stems grown in the light and in darkness. The results were consistent with the hypothesis that regulated growth of the cell wall depends on xyloglucan metabolism. Furthermore, the characterization of xyloglucan extracted from leaves of light-grown pea plants indicates that xyloglucan metabolism is tissue specific. Changes in xyloglucan subunit structure observed in elongating stems are consistent with the in muro realization of a metabolic pathway that was previously proposed solely on the basis of the in vitro activities of plant glycosyl hydrolases.

Metabolomics Reveals Cu(OH)2 Nanopesticide-Activated Anti-oxidative Pathways and Decreased Beneficial Antioxidants in Spinach Leaves

While the use of nanopesticides in modern agriculture continues to increase, their effects on crop plants are still poorly understood. Here, 4 week old spinach plants grown in an artificial medium were exposed via foliar spray to Cu(OH)₂ nanopesticide (0.18 and 18 mg/plant) or Cu ions (0.15 and 15 mg/plant) for 7 days. A gas chromatography-time-of-flight-mass spectrometry metabolomics approach was applied to assess metabolic alterations induced by Cu(OH)₂ nanopesticide in spinach leaves. Exposure to Cu(OH)₂ nanopesticide and copper ions induced alterations in the metabolite profiles of spinach leaves. Compared to the control, exposure to 18 mg of Cu(OH)₂ nanopesticide induced significant reduction (29-85%) in antioxidant or defense-associated metabolites including ascorbic acid, α-tocopherol, threonic acid, β-sitosterol, 4-hydroxybutyric acid, ferulic acid, and total phenolics. The metabolic pathway for ascorbate and aldarate was disturbed in all exposed spinach plants (nanopesticide and Cu²⁺). Cu²⁺ is responsible for the reduction in antioxidants and perturbation of the ascorbate and aldarate metabolism. However, nitrogen metabolism perturbation was nanopesticide-specific. Spinach biomass and photosynthetic pigments were not altered, indicating that metabolomics can be a rapid and sensitive tool for the detection og earlier nanopesticide effects. Consumption of antioxidants during the antioxidant defense process resulted in reduction of the nutritional value of exposed spinach.

Radical-induced inactivation of kidney Na+,K(+)-ATPase: sensitivity to membrane lipid peroxidation and the protective effect of vitamin E

The Na+,K(+)-ATPase is a membrane-bound, sulfhydryl-containing protein whose activity is critical to maintenance of cell viability. The susceptibility of the enzyme to radical-induced membrane lipid peroxidation was determined following incorporation of a purified Na+,K(+)-ATPase into soybean phosphatidylcholine liposomes. Treatment of liposomes with Fenton's reagent (Fe2+/H2O2) resulted in malondialdehyde formation and total loss of Na+,K(+)-ATPase activity. At 150 microM Fe2+/75 microM H2O2, vitamin E (5 mol%) totally prevented lipid peroxidation but not the loss of enzyme activity. Lipid peroxidation initiated by 25 microM Fe2+/12.5 microM H2O2 led to a loss of Na+,K(+)-ATPase activity, however, vitamin E (1.2 mol%) prevented both malondialdehyde formation and loss of enzyme activity. In the absence of liposomes, there was complete loss of Na+,K(+)-ATPase activity in the presence of 150 microM Fe2+/75 microM H2O2, but little effect by 25 microM Fe2+/12.5 microM H2O2. The activity of the enzyme was also highly sensitive to radicals generated by the reaction of Fe2+ with cumene hydroperoxide, t-butylhydroperoxide, and linoleic acid hydroperoxide. Lipid peroxidation initiated by 150 microM Fe2+/150 microM Fe3+, an oxidant which may be generated by the Fenton's reaction, inactivated the enzyme. In this system, inhibition of malondialdehyde formation by vitamin E prevented loss of Na+,K(+)-ATPase activity. These data demonstrate the susceptibility of the Na+,K(+)-ATPase to radicals produced during lipid peroxidation and indicate that the ability of vitamin E to prevent loss of enzyme activity is highly dependent upon both the nature and the concentration of the initiating and propagating radical species.

Hydroxyl radical mediates the endothelium-dependent relaxation produced by bradykinin in mouse cerebral arterioles

Bradykinin relaxes arterioles on the brain's surface. This response is endothelium-dependent. The data presented here confirm the hypothesis that hydroxyl free radical mediates this response and may be the endothelium-dependent relaxing factor for bradykinin in this microvascular bed. The response to a locally applied bolus of bradykinin (80 micrograms/ml) was monitored by intravital TV microscopy. The response was significantly inhibited or totally blocked by the presence of superoxide dismutase 60 U/ml, catalase 46 U/ml, or deferoxamine 0.1 or 0.2 mM. The superoxide dismutase scavenges superoxide radical, which is known to enter the subarachnoid space as a consequence of cyclooxygenase activation. Cyclooxygenase is activated by bradykinin. The superoxide can form H2O2, scavenged by catalase, and the two together generate hydroxyl. The formation of hydroxyl radical is catalyzed by iron. Deferoxamine 0.1 mM scavenges the iron, blocking the generation of hydroxyl. Deferoxamine 0.2 mM also directly scavenges the hydroxyl. None of the pharmacologic probes had an effect on arteriolar diameter when locally applied without bradykinin. Since the dilation produced by bradykinin was inhibited or totally blocked by probes that prevented hydroxyl formation or directly scavenged hydroxyl radical, that radical is either an essential mediator of the arteriolar relaxation, or is the endothelium-dependent relaxing factor for bradykinin in pial arterioles.

Hydroxyl radical mediation of immune renal injury by desferrioxamine

The acute phase of glomerular injury in a model of antiglomerular basement membrane, antibody-induced glomerulonephritis (antiGBM-GN) in rabbits was shown to be neutrophil-dependent using nitrogen mustard depletion studies. Administration of desferrioxamine (DFX) prevented the development of proteinuria in this model of renal injury [24 hr protein excretion (mean +/- SEM): antiGBM-GN/DFX = 16.2 +/- 2.9 mg compared with antiGBM-GN control = 271.5 +/- 92.2 mg, P less than 0.01]. Antibody binding levels, glomerular filtration rates, circulating complement and neutrophil counts, glomerular C3 deposition, and neutrophil infiltration did not differ between DFX treated and antiGBM-GN groups. In vitro assay systems to assess oxygen radical production [superoxide anion (O2-) and hydroxyl radical (OH.)] by neutrophils activated via the interaction of antiGBM antibody, GBM and complement were established. In these assays, DFX inhibited OH. production by immunologically-stimulated neutrophils (ISN) [nM diphenol/hr/10(6) cells, mean +/- SEM, ISN/DFX = 8 +/- 2 compared with ISN = 191 +/- 22, P less than 0.01] while production of O2- was not affected [nM O2-/hr/10(6) cells, mean +/- SEM, ISN/DFX = 29.1 +/- 4.3 compared with ISN = 32.6 +/- 2.5, P greater than 0.05]. These studies demonstrate that the iron chelator desferrioxamine can prevent neutrophil-dependent immune renal injury by interfering with neutrophil function. Treatment with the hydroxyl radical scavenger dimethylthiourea also significantly attenuated renal injury in antiGBM-GN. Together, the in vivo and in vitro data strongly suggest that neutrophil-dependent immunological renal injury is mediated via hydroxyl radical production by activated neutrophils within glomeruli.

Inactivation of alpha 1-antiproteinase by hydroxyl radicals. The effect of uric acid

The elastase-inhibitory activity of alpha 1-antiproteinase is inactivated by hydroxyl radicals (.OH) generated by pulse radiolysis or by reaction of iron ions with H2O2 in the presence of superoxide or ascorbate. Uric acid did not protect alpha 1-antiproteinase against inactivation by .OH in pulse radiolysis experiments or in the superoxide/iron/H2O2 system, whereas it did in systems containing ascorbic acid. We propose that radicals formed by attack of .OH on uric acid are themselves able to inactivate alpha 1-antiproteinase, but that these uric acid radicals can be 'repaired' by ascorbic acid.