A possible mechanism for vascular endothelial cell injury elicited by activated leukocytes: a significant involvement of adhesion molecules, CD11/CD18, and ICAM-1

To clarify the mechanism of vascular endothelial cell injury induced by activated leukocytes, we investigated the intracellular peroxide level in endothelial cells and the effect of antibodies against adhesion molecules on it. The change in the intracellular peroxide level was measured using the fluorescence of 2,7-dichlorofluorescein diacetate. The fluorescence intensity of the endothelial cells exposed to PMA-stimulated leukocytes increased with time up to 15 min, although neither PMA alone nor unstimulated leukocytes alone showed such increase at all. When catalase, which degrades hydrogen peroxide produced by leukocytes, was added to this system, the peroxide level in endothelial cells decreased significantly. On the other hand, pretreatment of endothelial cells with allopurinol, a specific inhibitor of xanthine oxidase, also caused significant inhibition of the increase in peroxide level in the endothelial cells. The monoclonal antibodies against CD11a, CD11b, CD18, and ICAM-1 showed almost complete inhibition of the increase in intracellular peroxide levels of the endothelial cells exposed to PMA-stimulated leukocytes. In contrast, the anti-CD11c antibody could not block the increase in fluorescence intensity due to peroxides. The endothelial injury elicited by activated leukocytes was partially inhibited by catalase alone (approximately 40%) and allopurinol alone (approximately 60%), but it was completely inhibited by the concomitant treatment of endothelial cells with catalase and allopurinol. The specific antibodies against such adhesion molecules as ICAM-1 and CD11/CD18 except CD11c/CD18 also blocked the endothelial cell injury significantly. These data suggest that there is a good correlation between the early increase in intracellular peroxides and endothelial cell injury elicited by PMA-stimulated leukocytes and that the adhesion of activated leukocytes to endothelial cells via CD11a/CD18-ICAM-1 must be deeply involved in these phenomena.

Free radicals in retinal and choroidal blood flow autoregulation in the piglet: interaction with prostaglandins

PURPOSE

To study the role of free radicals in autoregulation of retinal blood flow (RBF) and choroidal blood flow (ChBF) and the contribution of the cyclooxygenase pathway in free radical formation during blood pressure changes in 1- to 3-day-old pigs.

METHODS

Blood pressure was adjusted by inflating balloon-tipped catheters placed at the aortic isthmus and the aortic root to induce hypertension and hypotension, respectively. Blood flow was measured using the microsphere technique. Also, the effects of peroxides on retinal artery diameter were studied on eyecup preparations using time-frame photography processed by digital imaging.

RESULTS

Blood gases and intraocular pressure (13 +/- 1 mm Hg) remained stable throughout the experiments. In control animals, RBF was constant only between 30 and 75 mm Hg of ocular perfusion pressure and ChBF increased as a function of ocular perfusion pressure (tau = 0.58, P < 0.01). Inhibition of peroxidation with the free radical scavenger 21-aminosteroid U74389F (2.5 mg/kg) widened the range of RBF and ChBF autoregulation (ocular perfusion pressure from 30 to 131 mm Hg). Hypertension caused an increase in the products of peroxidation, malondialdehyde, and hydroperoxides, as well as in prostaglandin E2, prostaglandin F2 alpha, and 6-keto-prostaglandin F1 alpha in the retina and choroid of control animals; these changes were inhibited by the free radical scavengers U74389F (2.5 mg/kg) and high-dose allopurinol (140 mg/kg) as well as by the cyclooxygenase inhibitors ibuprofen (40 mg/kg) and indomethacin (5 mg/kg). In isolated eyecup preparations, H2O2 and cumene hydroperoxide dilated retinal vessels, and this effect was completely blocked by indomethacin.

CONCLUSIONS

These findings indicate that free radicals play a major role in setting the upper limit of RBF and ChBF autoregulation of the newborn animal. In addition, there exists a positive feedback interaction between free radicals and cyclooxygenase activity in ocular tissues, such that during hypertension the cyclooxygenase pathway is an important producer of free radicals and in turn is also activated by them.

[Respiratory diseases and oxidants]

Oxidants play a major role in mediating a variety of human disorders. The sources of oxidants may vary. They can be released by activated inflammatory cells or derive from the environment (such as pollution or tobacco smoke). In addition to acute, usually reversible reactions, numerous pulmonary diseases are associated with long lasting oxidant stress (adult respiratory distress syndrome, drug induced lung lesions, chronic obstructive pulmonary diseases, asthma, emphysema, interstitial fibrosis). Therapeutic action aimed at increasing anti-oxidant defense mechanisms is still a clinical challenge. Administration of N-acetylcysteine by the oral route is a simple and efficacious means of correcting oxidant-antioxidant imbalance.

Effects of peroxidation and aging on rat neocortical ACh-release and protein kinase C

Cerebral cortical synaptosomes were prepared from 2- or 24-month-old Fischer 344 rats and exposed to a peroxidizing condition (50 microM ferrous ions and 2 microM ascorbate ions) before measuring either the release of newly synthesized [3H]acetylcholine (ACh) or protein kinase C activity (PKC). Several secretagogues with different mechanisms of action and different responses to aging were used to trigger release: K+ depolarization (5 mM-60 mM), calcium ionophore A23187 (1-10 micrograms/ml), and 4-aminopyridine (0.1-10 mM). Aging reduced K+ depolarization-induced release at every K+ concentration studied, reduced A23187-induced release at low but not high concentrations and did not affect 4-aminopyridine-induced release. Membrane peroxidation of synaptosomes from 2-month-old rats altered the response to secretagogues to match that seen in 24-month-old rats. Membrane peroxidation also attenuated the A23187-stimulated translocation of free to bound synaptosomal PKC activity in 2-month-old but not 24-month-old animals. These results suggest that membrane peroxidation may mimic some age-related deficits in secretagogue-induced [3H]ACh release.

Coenzyme Q10, plasma membrane oxidase and growth control

The plasma membrane of eukaryotic cells contains an NADH oxidase which can transfer electrons across the membrane. This oxidase is controlled by hormones, growth factors and other ligands which bind to receptors in the plasma membrane. Oncogenes also affect activity of the oxidase. Natural serum components such as diferric transferrin and ceruloplasmin which stimulate proliferation also stimulate membrane oxidase activity. Additional growth factors can be required to complement the proliferative effect. Electron transport across the plasma membrane can be measured by the reduction of impermeable electron acceptors, such as ferricyanide, which also stimulate cell growth. The oxidants activate growth-related signals such as cytosolic alkalinization and calcium mobilization. Antiproliferative agents such as adriamycin and retinoic acid inhibit the plasma membrane electron transport. Flavin, Coenzyme Q and an iron chelate on the cell surface are apparent electron carriers for the transmembrane electron transport. Coenzyme Q10 stimulates cell growth, and Coenzyme Q analogs such as capsaicin and chloroquine reversibly inhibit both growth and transmembrane electron transport. Addition of iron salts to the depleted cells restores activity and growth. The ligand-activated oxidase in the plasma membrane introduces a new basis for control of signal transduction in cells. The redox state of the quinone in the oxidase is proposed to control tyrosine kinase either by generation of H2O2 or redox-induced conformational change.

Interaction between reactive oxygen species and coenzyme Q10 in an aprotic medium: a cyclic voltammetry study

The involvement of coenzyme Q (CoQ) as an antioxidant agent in several oxidative processes both in vitro and in vivo is nowadays pointed out by several biochemical and clinical studies, but the chemical mechanisms of this action are not yet unequivocally established. Electrochemistry provides very useful techniques for the analysis of the kinetics and thermodynamics, and mechanisms of chemical phenomena involving electron transfers, e.g. in the case of radical reactions. In the present study we used cyclic voltammetry to investigate the interactions between oxygen radicals and ubiquinone in aprotic medium, a condition similar to that existing in the biological membranes. The results obtained showed that ubiquinone is more easily reduced than oxygen, ruling out the possibility of an electron transfer from semiquinone to oxygen to produce superoxide radicals. On the contrary, it was demonstrated that fully reduced quinone is able to scavenge the superoxide radical, by reduction to peroxide ion, lowering actually the oxidative potential in the medium.

[Alteration of lipid peroxidation and the activity of peroxide metabolism enzymes in the liver, kidney and lung following the administration of paraquat in mice]

The sequential changes of the activity of peroxide metabolism enzymes and thiobarbituric acid reaction substance (TBARS) as an indicator of lipid peroxide concentration were observed to analyze the mechanisms of tissue injury due to the administration of paraquat in DDY mice. Each six mice were decapitated at 3, 6, 9, 12, 15, 18, 21 or 24 hours following the intraperitoneal administration of paraquat 60 mg.kg-1, and the liver, kidney and lung were removed and homogenized to quantify lipid peroxide concentration and the activity of peroxide metabolism enzymes. In the liver and kidney, TBARS increased gradually and reached the maximum level at 9 hours after the administration of paraquat in the liver and at 12 hours in the kidney. Significant increases in superoxide dismutase (SOD), glutathione peroxidase and catalase (CAT) activities were observed at 15 or 18 hours after the injection of paraquat. In the lung, lipid peroxide concentration decreased significantly and the activities of SOD and CAT increased at 15 hours after injection of paraquat. TBARS in serum started to increase at 9 hours after the administration of paraquat and reached the maximum level at 15 hours. These findings indicate that the induction of peroxide metabolism enzymes followed the increase of TBARS which was induced by paraquat in the liver and kidney. However, the enzyme induction was produced by paraquat without the increase of TBARS in the lung. Active oxygen radicals play an important role in the toxic action of paraquat and might produce the induction of peroxide metabolism enzymes following the administration of paraquat.

Peroxide dependence of the semisynthetic enzyme selenosubtilisin

Selenosubtilisin, a semisynthetic enzyme produced by chemical modification of subtilisin's catalytic serine, mimics the antioxidant enzyme glutathione peroxidase, catalyzing the reduction of hydroperoxides by 3-carboxy-4-nitrobenzenethiol. In analogy with the natural peroxidase, a variety of hydroperoxides are accepted as substrates for the semisynthetic enzyme, whereas the dialkyl compound tert-butyl peroxide is not. Kinetic investigations reveal that kmax is dependent upon the nature of the hydroperoxide, indicating that peroxide-mediated oxidation of the enzymic selenolate is at least partially rate-limiting. Experiments with the radical trap 2,6-di-tert-butyl-4-methylphenol suggest that, while the nonenzymic reaction between tert-butyl hydroperoxide and thiol involves free radicals, the same reaction catalyzed by selenosubtilisin does not. The studies described here support the enzyme's proposed ping-pong mechanism and are consistent with previous mechanistic observations.

Protection of retinal pigment epithelium from oxidative injury by glutathione and precursors

PURPOSE

This study was performed to examine the effect of exogenous glutathione (GSH) or its precursor amino acids on oxidative injury in cultured human retinal pigment epithelium (RPE).

METHODS

Cultured human RPE cells were suspended in Krebs-Henseleit medium, and 150 microM t-butylhydroperoxide was added. Cell viability was assessed by 0.2% trypan blue exclusion 30, 60, and 120 minutes after the addition of GSH or its amino acid precursors.

RESULTS

Added GSH provided protection at concentrations of 0.01 mM and higher. The amino acid precursors for GSH, glutamate, cysteine, and glycine also protected against injury, but this required at least 0.1 mM of each amino acid. Inhibition of intracellular GSH synthesis by inclusion of 1 mM buthionine sulfoximine eliminated the protection by added amino acids but did not alter the protection by added GSH.

CONCLUSIONS

These results indicate that protection by the amino acid precursors is mediated through synthesis of GSH, and they also show that exogenous GSH can provide protection against oxidative injury.

Rat liver heme oxygenase. High level expression of a truncated soluble form and nature of the meso-hydroxylating species

A rat heme oxygenase (HO-1) gene without the sequence coding for the last 23 amino acids has been constructed and expressed behind the pho A promoter in Escherichia coli. The enzyme is expressed at high levels as a soluble catalytically active protein that causes the bacterial cells to accumulate biliverdin. The purified truncated heme-heme oxygenase complex is spectroscopically indistinguishable from the complex with the native enzyme and converts heme to biliverdin when reconstituted with rat liver cytochrome P450 reductase. Reaction of the recombinant heme-heme oxygenase complex with H2O2 produces a species with the spectroscopic properties of verdoheme. Unidentified products are obtained when this intermediate is directly extracted from the protein, but biliverdin is obtained if the verdoheme-protein complex is exposed to cytochrome P450 reductase and NADPH before the extraction step. In contrast, reaction of the heme-heme oxygenase complex with meta-chloroperbenzoic acid (mCPBA), tert-butylhydroperoxide, or cumene hydroperoxide yields a ferryl (FeIV = O) complex. Reaction of the heme-heme oxygenase complex with mCPBA also produces an EPR-detectable protein radical. In accord with formation of a ferryl intermediate, recombinant heme oxygenase catalyzes the mCPBA- and alkylhydroperoxide-dependent peroxidation of 2-methoxyphenol (guaiacol). Guaiacol oxidation is not observed during turnover of the enzyme by cytochrome P450 reductase/NADPH or H2O2. Conversely, biliverdin is not formed with tert-butylhydroperoxide or mCPBA. H2O2 thus supports the first step of the normal catalytic oxidation of heme by heme oxygenase, but alkyl and acyl hydroperoxides do not. These results suggest that the alpha-meso-hydroxylation required for biliverdin formation is mediated by the distal of the two oxygens in the iron-dioxygen intermediate (Fe-O-O) engendered by reaction with either cytochrome P450 reductase/NADPH or H2O2.

Effect of the K+/H+ ionophore nigericin on response of A549 cells to photodynamic therapy and tert-butylhydroperoxide

The K+/H+ ionophore nigericin dramatically increases killing of V79 cells and A549 cells by photodynamic therapy (PDT) sensitized by chloroaluminum phthalocyanine. Previous studies suggested that the interaction between PDT and nigericin is related to the ability of this ionophore to reduce intracellular pH (pHi). The present study was undertaken to test the possibility that nigericin, by lowering pHi, inhibits reductive detoxification of PDT-produced peroxides by enzymes of the glutathione (GSH) redox cycle and the pentose cycle. To test this possibility we examined the effects of nigericin on the toxicity and metabolism of a model peroxide, tert-butylhydroperoxide (tert-BOOH), in A549 cells, a cell line in which the GSH redox cycle is known to be the principal pathway for reduction and detoxification of tert-BOOH. We found that nigericin equilibrates pHi of A549 cells with extracellular pH (pHe) in a time-dependent manner. It increases the toxicity of tert-BOOH toward A549 cells, inhibits loss of tert-BOOH from the buffer overlying the cells, and reduces the rate of 14CO2 release from radiolabelled glucose, which is a measure of pentose cycle activity. These effects are significantly greater at pHe 6.40 than at 7.40. Monensin, a Na+/H+ ionophore which does not reduce pHi, does not enhance the toxicity of tert-BOOH and has only a minimal effect on tert-BOOH reduction. These data suggest that nigericin-induced inhibition of peroxide detoxification is at least a plausible mechanism by which the ionophore might interact with PDT.

Protection by dihydroergocryptine of glutamate-induced neurotoxicity

Dihydroergocryptine is a hydrogenated ergot derivative with pharmacological actions mainly related to its dopaminomimetic activity. Here we report that dihydroergocryptine can protect cultured rat cerebellar granule cells against glutamate-induced neurotoxicity, assessing cell viability with the fluorescein diacetate-propidium iodide technique. Dihydroergocryptine antagonized both the neuronal death produced by acute exposure to a toxic glutamate concentration as well as the normal age-dependent degeneration in culture. The effect of dihydroergocryptine might be mediated by a scavenger action as suggested by the fact that the compound in a concentration-dependent manner reduced the formation of intracellular peroxides produced in cerebellar granule cells by exposure to 100 microM glutamate. This action is apparently not mediated entirely by interactions with the dopamine D2 receptors. The neuroprotective action suggests that dihydroergocryptine might be a potential useful drug in the therapy and/or prophylaxis of acute and chronic neurodegenerative diseases related to excitotoxic damage.

Free radicals in the genesis of Alzheimer's disease

As part of an ongoing investigation of the role of oxygen free radicals in Alzheimer's disease (AD), the formation of peroxidation products, the activities of free radical defense enzymes, and the level of total iron were determined in autopsy brain tissue from donors with AD and from age-matched non-demented donors. Calcium uptake was also investigated in mitochondria harvested from fibroblasts grown in tissue culture from skin samples taken from brain donors. Compared to controls, homogenates of AD frontal cortex produced elevated levels of peroxidation products and this difference was amplified in a dose-dependent manner by iron (1 to 200 microM). Peroxidation produced by 200 microM iron was reduced dose dependently by the lazaroid U-74500A. The IC50 was 10 microM in AD cortex and 2.5 microM in controls. Superoxide dismutase (SOD), one of the free radical defensive enzymes, was reduced by 25 to 35% in AD frontal cortex, hippocampus and cerebellum. In other brain areas, SOD did not differ between AD and control. The activities of catalase and glutathione peroxidase were the same in AD and control samples. Endogenous iron levels were higher in AD frontal cortex (2.5 nmol/mg protein) than in controls (1.5 nmol/mg protein). Calcium uptake by AD fibroblast mitochondria is 50% lower than in controls under basal conditions. Following exposure to 200 microM iron, mitochondrial calcium uptake is increased by 58% in AD and by 38% in controls. Pretreatment with 200 microM U-74500A or 1 mM deferoxamine, prior to exposure to 200 microM iron, gave complete protection to control mitochondria but gave only partial protection to AD mitochondria. These studies indicate that in AD, both CNS and peripheral cells show increased sensitivity to oxygen free radicals. The source of this increased sensitivity has not yet been identified but could reflect either reduced free radical defenses or increased free radical formation or both. Work is underway using electron paramagnetic resonance spectrometry to determine in vivo, premortem free radical activity in AD patients.

Trypanothione-dependent peroxide metabolism in Trypanosoma cruzi different stages

Different stages of Trypanosoma cruzi are able to metabolize low concentrations of H2O2. Trypomastigotes showed a higher initial rate per mg protein than amastigotes or epimastigotes derived from them. Amastigotes could metabolize H2O2 at a lower rate than the other developmental stages of T. cruzi. A peroxide-metabolizing activity was detected in extracts of T. cruzi epimastigotes. This 'NADPH peroxidase' activity was lost upon dialysis of the extracts and was probably due to a non-enzymatic reaction(s) with endogenous dihydrotrypanothione (T(SH)2) and/or other thiols, thus explaining the inhibition of H2O2 metabolism in intact cells by thiol inhibitors. An amount of non-protein thiols equivalent to an intracellular concentration of 2.0-3.0 mM was found in epimastigotes, which is sufficient to account for the rate of NADPH oxidation observed in the presence of high concentration of peroxides (> 100 microM). Addition of T(SH)2 increased this rate, implying that this thiol could be used as a substrate in that reaction. In addition, this activity was hardly detectable in the extracts in the presence of low concentration of peroxides (< 20 microM), indicating a high Km, which would be incompatible with a true peroxidase activity. Taking into account the high intracellular concentration of thiols measured, this activity probably accounted for the rates of H2O2 metabolism detected in intact T. cruzi. These results also confirm that T. cruzi is an organism with limited ability to detoxify H2O2.

Inhibitory effects of semisynthetic flavonoid derivatives on the biochemical markers of tumor promotion in mouse epidermis in vivo

Two sets of flavonoid derivatives were synthesized from condensed tannins (CTs) or catechin, and compared with the procyanidin monomer models, (+)-catechin and (-)-epicatechin, for their abilities to inhibit the biochemical effects of the potent tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in mouse epidermis in vivo. Topical applications of the semisynthetic flavonoids, catechin dialkyl ketals and epicatechin-4-alkylsulphides inhibit TPA-induced ornithine decarboxylase (ODC) activity to a much greater degree than catechin or epicatechin. Moreover, they reduce TPA-stimulated hydroperoxide (HPx) production, a response that cannot be inhibited by catechin or epicatechin. These compounds also inhibit the sequential stimulations of protein and DNA synthesis linked to TPA promotion. The remarkable effectiveness of these synthetic compounds, especially against the ODC marker of skin tumor promotion, suggests that they may be effective anti-tumor promoters.

Interaction of adriamycin aglycones with isolated mitochondria. Effect of selenium deficiency

Adriamycin (AdM) aglycones have dramatic effects on isolated heart mitochondria, oxidizing pyridine nucleotides, modifying sulfhydryl groups, and triggering a permeability transition of the inner membrane that results in free passage of solutes smaller than 1500 Da. In this investigation, the role of glutathione (GSH) peroxidase in these actions of the aglycones was evaluated, by comparing mitochondria from selenium-deficient and selenium-supplemented rats, with the following results. Selenium deficiency was without effect on the permeability transition of heart mitochondria, followed via Ca2+ release and triggered by AdM aglycone or by t-butyl hydroperoxide (TBH) or H2O2, both of which are authentic substrates of the peroxidase. The permeability transition of liver mitochondria was delayed by selenium deficiency regardless of the triggering agent; however, substantial triggering by the aglycone and TBH persisted in mitochondria from selenium-deficient animals. Selenium deficiency inhibited thiol modification elicited by AdM aglycone and H2O2 in heart mitochondria and by the aglycone, TBH, and possibly H2O2 in liver mitochondria. It would thus appear that AdM aglycone, TBH, and H2O2 can induce the permeability transition of isolated heart mitochondria via a process (or processes) distinct from the catalytic activity of the peroxidase. Furthermore, even in liver, where involvement of the peroxidase is observed, mechanisms other than the GSH cycle can contribute to transition induction by the aglycone and by TBH. Finally, mitochondrial-SH group modification by the aglycones appeared not to be causally linked to induction of the permeability transition. This laboratory has suggested that the effects of aglycone metabolites of AdM on mitochondria mediate the cardiotoxicity that limits use of the parent drug. The data presented in this paper argue against the involvement of GSH peroxidase in that process. They are in agreement with in vivo studies, which have generally failed to find evidence for amelioration of AdM cardiotoxicity in selenium-deficient animals.

A method for defining the stages of low-density lipoprotein oxidation by the separation of cholesterol- and cholesteryl ester-oxidation products using HPLC

A new high-performance liquid chromatographic system for the identification of some of the lipid oxidation products of low-density lipoprotein (LDL) oxidized by copper is described. Using a reversed-phase C-18 column and an isocratic solvent system of acetonitrile/isopropanol/water (44/54/2, v/v/v), a number of oxidized lipid moieties were resolved and detected simply by their 234-nm absorbance. The nature of several of these compounds was determined by chromatographic criteria, chemiluminescence, and mass spectrometry. The production of compounds within 4 h oxidation corresponded to the production of lipid hydroperoxides, the quantitatively most important of which is cholesteryl linoleate hydroperoxide, and to the rapid decrease in the cholesteryl ester content of LDL detected at 210 nm. More prolonged copper oxidation (up to 48 h) of LDL resulted in decreased quantities of lipid hydroperoxide moieties and increased amounts of a number of other, nonhydroperoxide, compounds. 7-Ketocholesterol and cholesterol linoleate hydroxide are two of the major products of prolonged oxidation. The detection of oxidation products correlates with the modification of LDL protein, permits a four-stage definition of metal-mediated LDL oxidation, and enables the calculation of a quantitative index of oxidation (lipoprotein oxidation index). This method will be generally applicable to cell- and copper-mediated oxidation, and will enable standardization of, and direct comparison between, different preparations of oxidized LDL.

Free radical formation in isolated murine keratinocytes treated with organic peroxides and its modulation by antioxidants

Electron paramagnetic resonance spin-trapping has been used to study the production of free radicals from tert-butyl hydroperoxide, tert-butyl peroxybenzoate, cumene hydroperoxide and ethyl hydroperoxide in isolated murine keratinocytes. Free radical species could be trapped from keratinocytes treated with all peroxides, with radicals produced from both one-electron oxidative and reductive pathways. The hindered phenolic antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), which are known to inhibit peroxide-induced tumour promotion in vivo, decreased the amount of radical adduct production at a concentration of 10 mM, with BHA being significantly more effective than BHT. That all the peroxides in this study produced free radicals in keratinocytes, and that BHA and BHT decreased the amounts of radicals trapped, suggests that free radical production by organic peroxide compounds is involved in their in vivo tumour-promoting activity.

Iron-reducing and free-radical-scavenging properties of apomorphine and some related benzylisoquinolines

The scavenging and iron-reducing properties of a series of benzylisoquinolines of natural and synthetic origin have been studied. Bulbocapnine, boldine, glaucine, and stepholidine acted as scavengers of hydroxyl radical in the deoxyribose degradation by Fe(3+)-EDTA + H2O2. On the contrary, laudanosoline, apomorphine, protopapaverine, anonaine, and tetrahydroberberine increased deoxyribose degradation by a mechanism related to generation of superoxide anion. Only apomorphine had a stimulating effect in the system using citrate instead of ethylenediaminetetraacetic acid (EDTA) as well as in the absence of chelator. Apomorphine also stimulated DNA damage by Cu2+. The iron-ion reducing ability of apomorphine and laudanosoline was confirmed using cytochrome c. Both compounds scavenged peroxyl radicals in an aqueous medium, while in Fe(3+)-induced microsomal lipid peroxidation apomorphine acted as an inhibitor and laudanosoline stimulated the process. It is suggested that in microsomes the chain-breaking antioxidant properties of apomorphine overcome its possible influence on redox cycling of iron, or prooxidant properties.

Free radical formation in murine skin treated with tumour promoting organic peroxides

The generation of free radicals from tumour-promoting organic peroxides applied to intact murine skin samples has been studied by EPR spectroscopy using two techniques: first direct observation of ascorbyl radicals produced from reactions of peroxide-related radicals with ascorbate, an important endogenous antioxidant, and secondly, observation of radical adducts produced by spin-trapping. Free radical generation from tumour-promoting organic peroxides can be seen to occur in intact skin tissue through a one-electron reductive pathway, and takes place at sites including the viable cells of the epidermis and/or dermis. This radical generation is dependent upon the penetration of the skin by the peroxides, with the stratum corneum representing a major diffusional barrier to their penetration of skin. The technique of using ascorbyl radical measurement by EPR spectroscopy as a means of studying and quantifying radical production in intact tissues, developed in this work, may prove of much use in the study of many free radicals and their reactions in a wide range of biological systems, particularly skin. When combined with appropriate spin-trapping techniques, which enable identification of radical species and elucidation of their mechanisms of production, this enables the direct, real-time observation of radical reactions and mechanisms not previously possible in intact tissue samples.

Phenylbutazone peroxidatic metabolism and conjugation

Phenylbutazone, a nonsteroidal anti-inflammatory drug, elicits therapeutic as well as toxic effects by unknown pathways. Phenylbutazone was shown to form a conjugate with the heterocyclic amine bladder carcinogen 2-amino-4-(5-nitro-2-furyl)-thiazole (ANFT). To understand further the reactivity of these compounds, this study was conducted to identify the conjugate formed and determine the mechanism of conjugate formation. Both prostaglandin H synthase and horseradish peroxidase catalyzed conjugate formation. This conjugate was identified by 1H-NMR to be 4-[2-amino-4-(5-nitro-2-furyl)-5-thiazolyl]-4-butyl-1,2-diphenyl-3,5- pyrazolidinedione. Phenylbutazone-mediated oxygen uptake was inhibited by ANFT (0.1 mM) and the spin traps 5,5-dimethyl-1-pyrroline-N-oxide (200 mM) and tert-nitrosobutane (4 mM). By contrast, phenol (0.005 to 0.25 mM) and aminopyrine (0.4 mM) stimulated oxygen uptake. None of these agents mediated oxygen uptake in the absence of phenylbutazone. Conjugate formation was significantly increased by phenol (0.005-0.25 mM) and aminopyrine (0.4 mM), as well as in the absence of oxygen. Conjugate formation was inhibited by 5,5-dimethyl-1-pyrroline-N-oxide (200 mM), tert-nitrosobutane (4 mM), ascorbic acid (2 mM), and 95% oxygen. Horseradish peroxidase initiated conjugate formation at much lower concentrations than it metabolized ANFT. The stoichiometric relationship between phenylbutazone and ANFT, with respect to conjugate formation, was complex. With the concentration of ANFT fixed at 0.05 mM, phenylbutazone exhibited saturation kinetics with a Km of 0.2 mM. In contrast, saturation kinetics were not observed with ANFT.Km values for ANFT varied with the concentration of phenylbutazone used.(ABSTRACT TRUNCATED AT 250 WORDS)

Free radical production during metabolism of organic hydroperoxides by normal human keratinocytes

Evidence of a relationship between tumor production induced by various organic (hydro)peroxides and free radical formation has been shown in cultured murine keratinocytes and human skin-tumor cell line. In the present study the bioactivation of cumene hydroperoxide, t-butyl-hydroperoxide, and benzoyl peroxide via one-electron oxidation or reduction was compared in freshly isolated and in cultured normal human keratinocytes. The formation of methyl free radicals during the metabolism of cumene and t-butyl-hydroperoxide was shown by the electron spin resonance-spin trapping technique. Radical formation increased under hypoxic conditions. An intracellular activation site was demonstrated by the use of two spin-trapping agents, the hydrophilic, membrane-impermeable, 3,5-dibromo-4-nitrosobenzenesulfonic acid and the lipophilic, membrane-permeable alpha-(4-pyridyl-1-oxide)-N-t-butylnitrone. At 30 min incubation and 25 mM concentration, hydroperoxides exhibited cytotoxicity, as indicated by trypan blue exclusion and lactate dehydrogenase release assay; free radicals were concurrently trapped. Hydroperoxides at a lower concentration (1 mM) did not significantly affect cell viability. However, free radical production was still detected using a membrane-permeable spin trap. The incubation of keratinocytes with benzoyl peroxide did not show any peroxide-dependent radical adduct. No significant differences in bioactivation capability were demonstrated between freshly isolated and cultured human keratinocytes. The results indicate that cultured human keratinocytes can be used as a model system for the study of the metabolic activation to free radical intermediates of toxic and carcinogenic compounds in the epidermis.

Plasma glutathione peroxidase reduces phosphatidylcholine hydroperoxide

The reducing activity of rat plasma glutathione peroxidase on phosphatidylcholine hydroperoxide (PC-OOH) and cholesteryl ester hydroperoxide (CE-OOH) was examined since these hydroperoxides are the major oxidation products of plasma. PC-OOH was reduced by the enzyme while CE-OOH was not. The reduction of PC-OOH by the enzyme ceased when all thiol was consumed, but the activity was recovered by the addition of glutathione, suggesting glutathione is important to keep the enzyme in the reduced form. These results are consistent with the findings that CE-OOH is present in human and rat plasmas while PC-OOH is undetectable and suggest that one of the physiological roles of the enzyme is to reduce PC-OOH.