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R Cueto

Publications and source records attributed to R Cueto.

At least 19 recordsLinked to original sources
PubMed2001

Quinoid redox cycling as a mechanism for sustained free radical generation by inhaled airborne particulate matter.

The health effects of airborne fine particles are the subject of government regulation and scientific debate. The aerodynamics of airborne particulate matter, the deposition patterns in the human lung, and the available experimental and epidemiological data on health effects lead us to focus on airborne particulate matter with an aerodynamic mean diameter less than 2.5 microm (PM(2.5)) as the fraction of the particles with the largest impact in health. In this article we present a novel hypothesis to explain the continuous production of reactive oxygen species produced by PM(2.5) when it is deposited in the lung. We find PM(2.5) contains abundant persistent free radicals, typically 10(16) to 10(17) unpaired spins/gram, and that these radicals are stable for several months. These radicals are consistent with the stability and electron paramagnetic resonance spectral characteristics of semiquinone radicals. Catalytic redox cycling by semiquinone radicals is well documented in the literature and we had studied in detail its role on the health effects of cigarette smoke particulate matter. We believe that we have for the first time shown that the same, or similar radicals, are not confined to cigarette smoke particulate matter but are also present in PM(2.5). We hypothesize that these semiquinone radicals undergo redox cycling, thereby reducing oxygen and generating reactive oxygen species while consuming tissue-reducing equivalents, such as NAD(P)H and ascorbate. These reactive oxygen species generated by particles cause oxidative stress at sites of deposition and produce deleterious effects observed in the lung.

Air Pollutants↗
PubMed2001

Role of free radicals in the toxicity of airborne fine particulate matter.

Exposure to airborne fine particles (PM2.5) is implicated in excess of 50 000 yearly deaths in the USA as well as a number of chronic respiratory illnesses. Despite intense interest in the toxicity of PM2.5, the mechanisms by which it causes illnesses are poorly understood. Since the principal source of airborne fine particles is combustion and combustion sources generate free radicals, we suspected that PM2.5 may contain radicals. Using electron paramagnetic resonance (EPR), we examined samples of PM2.5 and found large quantities of radicals with characteristics similar to semiquinone radicals. Semiquinone radicals are known to undergo redox cycling and ultimately produce biologically damaging hydroxyl radicals. Aqueous extracts of PM2.5 samples induced damage to DNA in human cells and supercoiled phage DNA. PM2.5-mediated DNA damage was abolished by superoxide dismutase, catalase, and deferoxamine, implicating superoxide radical, hydrogen peroxide, and the hydroxyl radical in the reactions inducing DNA damage.

Air Pollutants↗
PubMed2000

Reaction of uric acid with peroxynitrite and implications for the mechanism of neuroprotection by uric acid.

Peroxynitrite, a biological oxidant formed from the reaction of nitric oxide with the superoxide radical, is associated with many pathologies, including neurodegenerative diseases, such as multiple sclerosis (MS). Gout (hyperuricemic) and MS are almost mutually exclusive, and uric acid has therapeutic effects in mice with experimental allergic encephalomyelitis, an animal disease that models MS. This evidence suggests that uric acid may scavenge peroxynitrite and/or peroxynitrite-derived reactive species. Therefore, we studied the kinetics of the reactions of peroxynitrite with uric acid from pH 6.9 to 8.0. The data indicate that peroxynitrous acid (HOONO) reacts with the uric acid monoanion with k = 155 M(-1) s(-1) (T = 37 degrees C, pH 7.4) giving a pseudo-first-order rate constant in blood plasma k(U(rate))(/plasma) = 0.05 s(-1) (T = 37 degrees C, pH 7.4; assuming [uric acid](plasma) = 0.3 mM). Among the biological molecules in human plasma whose rates of reaction with peroxynitrite have been reported, CO(2) is one of the fastest with a pseudo-first-order rate constant k(CO(2))(/plasma) = 46 s(-1) (T = 37 degrees C, pH 7.4; assuming [CO(2)](plasma) = 1 mM). Thus peroxynitrite reacts with CO(2) in human blood plasma nearly 920 times faster than with uric acid. Therefore, uric acid does not directly scavenge peroxynitrite because uric acid can not compete for peroxynitrite with CO(2). The therapeutic effects of uric acid may be related to the scavenging of the radicals CO(*-)(3) and NO(*)(2) that are formed from the reaction of peroxynitrite with CO(2). We suggest that trapping secondary radicals that result from the fast reaction of peroxynitrite with CO(2) may represent a new and viable approach for ameliorating the adverse effects associated with peroxynitrite in many diseases.

Bicarbonates↗
PubMed1999

Simple and rapid visual sensing of saccharides.

Solutions of compound 1 exhibit dramatic, characteristic color changes in response to sugar analytes. Structurally related saccharides including glucose phosphates and amino and carboxylic acid sugars can be readily distinguished by visual inspection. These findings should promote the design of unique color sensory materials based on readily available, functional macrocyclic hosts.

Benzhydryl Compounds↗
PubMed1999

Direct and simultaneous ultraviolet second-derivative spectrophotometric determination of nitrite and nitrate in preparations of peroxynitrite.

We have determined the initial concentrations of nitrite and nitrate for three different methods of synthesizing peroxynitrite using an ultraviolet second-derivative spectroscopy method (Fig. 3). As expected, the net nitrogen balance in these preparations (Fig. 4) and the yields of nitrite and nitrate (Table II) indicate that, at pH 6.0, peroxynitrite decomposes to give essentially NO3-. Stock solutions of peroxynitrite prepared using method I (ozonation of azide) consistently contain more NO2- and NO3- than method II (isoamyl nitrite with hydrogen peroxide) and method III (hydrogen peroxide with nitrous acid). Method II gives the least amount of NO2- contaminants, and NO3- impurities are the lowest in method III (Table I).

Animals↗
PubMed1999

Beta carotene and its oxidation products have different effects on microsome mediated binding of benzo[a]pyrene to DNA.

The effects of beta-carotene (betaC) and its oxidation products on the binding of benzo[a]pyrene (BaP) metabolites to calf thymus DNA was investigated in the presence of rat liver microsomes. Mixtures of betaC oxidation products (betaCOP) as well as separated, individual betaC oxidation products were studied. One set of experiments, for example, involved the use of the mixture of betaCOP obtained after a 2-h radical-initiated oxidation. For this data set, the incorporation of unoxidized betaC into microsomal membranes caused the level of binding of BaP metabolites to DNA to decrease by 29% over that observed in the absence of betaC; however, the incorporation of the mixture of betaCOP caused the binding of BaP metabolites to DNA to increase 1.7-fold relative to controls without betaC. Two variations of this experiment were studied: (1) When no NADPH was added, betaC decreased the binding of BaP metabolites to DNA by 19%, but the mixture of betaCOP increased binding by 3.3-fold relative to that observed in the absence of betaC. (2) When NADPH was added under near-anaerobic conditions, betaC caused an almost total (94%) decrease in binding whereas betaCOP had no effect on the amount of binding relative to that observed in the absence of betaC. Both betaCOP and cumene hydroperoxide caused BaP metabolites to bind to DNA even when NADPH was omitted from the incubation mixture. Separation of the mixture of betaC oxidation products into fractions by HPLC allowed preliminary testing of individual betaC oxidation products separately; of the various fractions tested, the products tentatively identified as 11,15'-cyclo-12,15-epoxy-11,12,15,15'-tetrahydro-beta-carotene and beta-carotene-5,6-epoxide appeared to cause the largest increase in BaP-DNA binding. Microsomes from rats induced with 3-methylcholanthrene (3MC) or Aroclor 1254 produced different levels of binding in some experimental conditions. We hypothesize that, under some conditions, the incorporation of betaC into microsomal membranes can be protective against P450-catalyzed BaP binding to DNA; however, the incorporation of betaCOP facilitates the formation of BaP metabolites that bind DNA, although only certain P450 isoforms catalyze the binding process.

Animals↗
PubMed1999

Antioxidant transport modulates peripheral airway reactivity and inflammation during ozone exposure.

We examined the effects of ozone (O(3)) and endogenous antioxidant transport on canine peripheral airway function, central airway function, epithelial integrity, and inflammation. Dogs were either untreated or pretreated with probenecid (an anion-transport inhibitor) and exposed for 6 h to 0.2 parts/million O(3). Peripheral airway resistance (Rpa) and reactivity (DeltaRpa) were monitored in three sublobar locations before and after exposure to either air or O(3). Pulmonary resistance and transepithelial potential difference in trachea and bronchus were also recorded. Bronchoalveolar lavage fluid (BALF) was collected before, during, and after exposure. O(3) increased Rpa and DeltaRpa only in probenecid-treated dogs and in a location-dependent fashion. Pulmonary resistance and potential difference in bronchus increased after O(3) exposure regardless of treatment. O(3) markedly increased BALF neutrophils only in untreated dogs. With the exception of hexanal, O(3) did not alter any BALF constituent examined. Probenecid reduced BALF ascorbate, BALF protein, and plasma urate. We conclude that 1) a 6-h exposure to 0.2 parts/million O(3) represents a subthreshold stimulus in relation to its effects on peripheral airway function in dogs, 2) antioxidant transport contributes to the maintenance of normal airway tone and reactivity under conditions of oxidant stress, 3) O(3)-induced changes in Rpa and DeltaRpa are dependent on location, and 4) peripheral airway hyperreactivity and inflammation reflect independent responses to O(3) exposure. Finally, although anion transport mitigates the effect of O(3) on peripheral airway function, it contributes to the development of airway inflammation and may represent a possible target for anti-inflammatory prevention or therapy.

Airway Resistance↗
PubMed1999

Ozone exposure increases aldehydes in epithelial lining fluid in human lung.

We hypothesized that exposure of healthy humans to ozone causes both ozonation and peroxidation of lipids in lung epithelial lining fluid. Twelve smokers and 15 nonsmokers (eight lung function "responders" and seven "nonresponders") were exposed once to air and twice to 0. 22 ppm ozone for 4 h with exercise in an environmental chamber, with each exposure separated by at least 3 wk. Bronchoalveolar lavage (BAL) was performed immediately after one ozone exposure and 18 h after the other ozone exposure. BAL fluid was analyzed for the aldehyde products of ozonation and lipid peroxidation, nonanal (C9) and hexanal (C6), as well as total protein, albumin, and immunoglobulin M as markers of changes in epithelial permeability. Ozone exposure resulted in a significant early increase in C9 (p = 0. 0001), with no statistically significant relationship between increases in C9 and lung function changes, airway inflammation, or changes in epithelial permeability. Increases in C6 levels were not statistically significant (p = 0.16). Both C9 and C6 levels returned to baseline by 18 h after exposure. These studies confirm that exposure to ozone with exercise, at concentrations relevant to urban outdoor air, results in ozonation of lipids in the airway epithelial lining fluid of humans.

Adolescent↗
PubMed1999

Aldehydes (nonanal and hexanal) in rat and human bronchoalveolar lavage fluid after ozone exposure.

We hypothesized that exposure of healthy humans to ozone at concentrations found in ambient air causes both ozonation and peroxidation of lipids in lung epithelial lining fluid. Smokers (12) and nonsmokers (15) were exposed once to air and twice to 0.22 ppm ozone for four hours with exercise in an environmental chamber; each exposure was separated by at least three weeks. Bronchoalveolar lavage (BAL) was performed immediately after one ozone exposure and 18 hours after the other ozone exposure. Lavage fluid was analyzed for two aldehyde products of ozonation and lipid peroxidation, nonanal and hexanal, as well as for total protein, albumin, and immunoglobulin M (IgM) as markers of changes in epithelial permeability. Ozone exposure resulted in a significant early increase in nonanal (p < 0.0001), with no statistically significant relationship between increases in nonanal and lung function changes, airway inflammation, or changes in epithelial permeability. Increases in hexanal levels were not statistically significant (p = 0.16). Both nonanal and hexanal levels returned to baseline by 18 hours after exposure. These studies confirm that exposure to ozone with exercise at concentrations relevant to urban outdoor air results in ozonation of lipids in the airway epithelial lining fluid of humans.

Adult↗
PubMed1998

Overexpression of hMTH1 mRNA: a molecular marker of oxidative stress in lung cancer cells.

Human MutT homologue (hMTH1) mRNA was overexpressed in SV-40-transformed non-tumorigenic human bronchial epithelial cells (BEAS-2B cells) and in 11 out of 12 human lung cancer cell lines relative to normal human bronchial epithelial cells. Expression levels of hMTH1 mRNA were inversely proportional to cellular levels of 8-oxo-deoxyguanosine. Together, these results suggest that hMTH1 gene expression may represent a molecular marker of oxidative stress that could ultimately be used to elucidate the temporal relationships between oxidative stress, genomic instability and the development of lung cancer.

Adaptor Proteins, Signal Transducing↗
PubMed1998

O3-induced formation of bioactive lipids: estimated surface concentrations and lining layer effects.

Recent evidence suggests that inhaled ozone (O3) does not induce toxicity via direct epithelial interactions. Reactions with epithelial lining fluid (ELF) constituents limit cellular contact and generate products, including lipid ozonation products, postulated to initiate pathophysiological cascades. To delineate specific aspects of lipid ozonation product formation and to estimate in situ surface concentrations, we studied the O3 absorption characteristics of ELF constituent mixtures and measured hexanal, heptanal, and nonanal yields as a function of ascorbic acid (AH2) concentration. Exposures of isolated rat lungs, bronchoalveolar lavage fluid (BALF) and egg phosphatidylcholine (PC) liposomes were conducted. 1) O3 absorption by AH2, uric acid, and albumin exceeded that by egg PC and glutathione. O3 reaction with egg PC occurred when AH2 concentrations were reduced. 2) Aldehydes were produced in low yield during lung and BALF exposures in a time- and O3 concentration-dependent manner. 3) Diminishing BALF AH2 content lowered O3 uptake but increased aldehyde yields. Conversely, AH2 addition to egg PC increased O3 uptake but reduced aldehyde yields. Estimations of bioactive ozonation and autoxidation product accumulation within the ELF suggested possible nanomolar to low micromolar concentrations. The use of reaction products as metrics of O3 exposure may have intrinsic sensitivity and specificity limitations. Moreover, due to the heterogenous nature of O3 reactions within the ELF, dose-response relationships may not be linear with respect to O3 absorption.

Absorption↗
PubMed1997

Carbon dioxide modulation of hydroxylation and nitration of phenol by peroxynitrite.

We have examined the formation of hydroxyphenols, nitrophenols, and the minor products 4-nitrosophenol, benzoquinone, 2,2'-biphenol, and 4,4'-biphenol from the reaction of peroxynitrite with phenol in the presence and absence of added carbonate. In the absence of added carbonate, the product yields of nitrophenols and hydroxyphenols have different pH profiles. The rates of nitration and hydroxylation also have different pH profiles and match the trends observed for the product yields. At a given pH, the sum of the rate constants for nitration and hydroxylation is nearly identical to the rate constant for the spontaneous decomposition of peroxynitrite. The reaction of peroxynitrite with phenol is zero-order in phenol, both in the presence and absence of added carbonate. In the presence of added carbonate, hydroxylation is inhibited, whereas the rate of formation and yield of nitrophenols increase. The combined maximum yield of o- and p-nitrophenols is 20 mol% (based on the initial concentration of peroxynitrite) and is about fourfold higher than the maximal yield obtained in the absence of added carbonate. The o/p ratio of nitrophenols is the same in the presence and absence of added carbonate. These results demonstrate that hydroxylation and nitration occur via two different intermediates. We suggest that the activated intermediate formed in the isomerization of peroxynitrous acid to nitrate, ONOOH*, is the hydroxylating species. We propose that intermediate 1, O=N-OO-CO2-, or secondary products derived from it, is (are) responsible for the nitration of phenol. The possible mechanisms responsible for nitration are discussed.

Carbon Dioxide↗
PubMed1997

Inhibition of peroxynitrite-mediated oxidation of glutathione by carbon dioxide.

Peroxynitrite reacts with CO2 to from an adduct containing a weak O--O bond that can undergo homolytic and/or heterolytic cleavage to give other reactive intermediates. Because the peroxynitrite/CO2 reaction is fast and physiological concentrations of CO2 are relatively high, peroxynitrite-mediated oxidations of biological species probably involve the peroxynitrite-CO2 adduct and its subsequent reactive intermediates. We have examined the reaction of glutathione with peroxynitrite in the presence and absence of added bicarbonate. In the presence of added bicarbonate, CO2 competes with glutathione for peroxynitrite, resulting in a markedly decreased consumption of glutathione compared with that observed in the absence of added bicarbonate. However, the consumption of glutathione still is much higher than predicted from the assumption that the glutathione-peroxynitrite reaction is the only reaction that can consume glutathione in this system. These results suggest that glutathione partially, but not completely, traps intermediate(s) derived from the peroxynitrite and CO2 reaction. Some rate constants for the trapping of the intermediates are estimated by simulating the reactions, and possible mechanisms for the reaction of peroxynitrite with glutathione in the presence of added bicarbonate are discussed.

Bicarbonates↗
PubMed1997

Peroxynitrite-mediated oxidation of D,L-selenomethionine: kinetics, mechanism and the role of carbon dioxide.

Peroxynitrite oxidizes D,L-selenomethionine (MetSe) by two competing mechanisms, a one-electron oxidation that leads to ethylene and a two-electron oxidation that gives methionine selenoxide (MetSeO). Kinetic modeling of the experimental data suggests that both peroxynitrous acid and the peroxynitrite anion react with MetSe to form MetSeO with rate constants of 20,460 +/- 440 M-1 s-1 and 200 +/- 170 M-1 s-1, respectively at 25 degrees C. The enthalpy (delta H++) and entropy (delta S++) of activation for the reaction of peroxynitrous acid with MetSe at pH 4.6 are 2.55 +/- 0.08 kcal mol-1 and -30.5 +/- 0.3 cal mol-1 K-1, respectively. With increasing concentrations of MetSe at pH 7.4, the yield of ethylene decreases and that of MetSeO increases, suggesting, as with methionine, the reactions leading to ethylene and MetSeO have different kinetic orders. We propose that the activated form of peroxynitrous acid, HOONO*, is the one-electron oxidant and ground-state peroxynitrite is the two-electron oxidant in the reaction of peroxynitrite with MetSe. The peroxynitrite anion rapidly adds to CO2 to form an adduct, O = N-OO-CO2- (1), capable of generating potent reactive species, and we therefore examined the role of CO2 in the peroxynitrite/MetSe system. In presence of added bicarbonate, the yield of ethylene obtained from the reaction of 0.4 mM peroxynitrite with 1.0 mM MetSe increases slightly with an increase in the concentration of bicarbonate from 0 to 5.0 mM and remains constant with a further increase of bicarbonate up to 20 mM. The yield of MetSeO, from the reaction of 10 mM peroxynitrite with 10 mM MetSe, decreases by 35% with an increase in the concentration of bicarbonate from 0 to 25 mM. Kinetic simulations show that the decrease in the yield of MetSeO is due to reaction of the peroxynitrite anion with CO2. These results suggest that CO2 partially protects MetSe from peroxynitrite-mediated oxidation and that 1 or its derivatives do not mediate the oxidation of MetSe to MetSeO.

Carbon Dioxide↗
PubMed1996

Detection of aldehydes in bronchoalveolar lavage of rats exposed to ozone.

We report the detection of hexanal, heptanal, and nonanal in the bronchoalveolar lavage (BAL) of rats exposed to 0.5 to 10 ppm ozone with or without simultaneous 5% CO2. These three aldehydes primarily result from the Criegee ozonation of specific mono- or polyunsaturated fatty acids that are present in significant amounts in the rat lung; e.g., palmitoleic acid gives heptanal, oleic gives nonanal, and linoleic and arachidonic can give hexanal. Hexanal also is produced in the ozone-initiated autoxidation of any n-6 polyunsaturated fatty acid, and thus is a measure of generalized oxidative stress. (Monounsaturated fatty acids do not undergo appreciable autoxidation.) This detection and quantitation of aldehydes directly demonstrates for the first time that unsaturated fatty acids undergo Criegee ozonation in the lung when ozone is inhaled. Exposure to ozone alone produced smaller apparent yields of the three aldehydes than did exposure to ozone plus 5% CO2. Hexanal, heptanal, and nonanal can be detected in BAL of rats 5 hr after the end of the ozone exposure, but after more than 5 hr only hexanal can be found, probably from ozone-induced autoxidation of n-6 PUFA that continues after ozone exposure. The measured amounts of aldehydes are low, and that, coupled with inherent biovariability, suggests that aldehydes may not be useful as quantitative dosimeters. However, they can be useful biomarkers, since some of these aldehydes (e.g., nonanal) are produced in ozone-specific pathways and aldehydes are the most easily detected among the lipid ozonation products (LOP). Furthermore, our identification of these aldehydes by BAL, coupled with our recognition that ozone itself cannot penetrate far enough into the lung to cause many of the effects associated with the inhalation of ozone, suggests that these aldehydes, as well as other types of LOP (such as hydroxyhydroperoxides and Criegee ozonides), may act as signal transduction molecules, activating lipases and causing the release of inflammatory molecules by a variety of pathways not yet entirely elucidated.

Aldehydes↗
PubMed1996

Rapid oxidation of DL-selenomethionine by peroxynitrite.

Peroxynitrite, the reaction product of nitric oxide and superoxide, rapidly oxidizes DL-selenomethionine (MetSe) with overall second-order kinetics, first-order in peroxynitrite and first-order in MetSe. The oxidation of MetSe by peroxynitrite goes by two competing mechanism. The first produces ethylene by what we propose to be a one-electron oxidation of MetSe. In the second mechanism, MetSe undergoes a two-electron oxidation that gives methionine selenoxide (MetSe = O); the apparent second-order rate constant, k2(app), for this process is (2.4 +/- 0.1) x 10(3) M-1s-1 at pH 7.4 and 25 degrees C. The kinetic modeling of the experimental data suggests that both peroxynitrous acid (k2 = 20,460 +/- 440 M-1s-1 at 25 degrees C) and the peroxynitrite anion (k3 = 200 +/- 170 M-1s-1 at 25 degrees C) are involved in the second-order reaction leading to selenoxide. These rate constants are 10- to 1,000-fold higher than those for the reactions of methionine (Met) with peroxynitrite. With increasing concentrations of MetSe at pH 7.4, the yield of ethylene decreases, while that of MetSe = O increases, suggesting that the reactions leading to ethylene and selenoxide have different kinetic orders. These results are analogous to those we previously reported for methionine and 2-keto-4-thiomethylbutanoic acid (KTBA),where ethylene is produced in a first-order reaction and sulfoxide in a second-order reaction. Therefore, we suggest that the reaction of peryoxynitrite with MetSe involves a mechanism similar to that we proposed for Met, in which an activated intermediate of peroxynitrous acid (HOONO) is the one-electron oxidant and reacts with first-order kinetics and ground-state peroxynitrite is the two-electron oxidant and reacts with second-order kinetics.

Chromatography, Gas↗
PubMed1996

Competitive reactions of peroxynitrite with 2'-deoxyguanosine and 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG): relevance to the formation of 8-oxodG in DNA exposed to peroxynitrite.

We have examined the formation of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) in reactions of peroxynitrite with 2'-deoxyguanosine (dG) and calf-thymus DNA. Peroxynitrite reacts with dG at neutral pH, but this reaction does not result in the buildup of 8-oxodG. We also do not find any evidence for the formation of 8-oxodG in calf-thymus DNA upon exposure to peroxynitrite. When 8-oxodG is mixed with 1000-fold excess dG and then allowed to react with peroxynitrite, about 50% of the 8-oxodG is destroyed. The preferential reaction of 8-oxodG is also evident when dG in calf-thymus DNA is partially oxidized in an Udenfriend system and then allowed to react with peroxynitrite. We suggest that 8-oxodG is not produced in peroxynitrite-mediated oxidations of dG and DNA or that it is produced but then is rapidly consumed in further reactions with peroxynitrite. Oxidized DNA bases frequently can be more oxidation sensitive than their corresponding progenitors and, therefore, may be present at] low steady-state concentrations and not represent stable markers of oxidative stress status. The importance of the 8-oxodG/peroxynitrite reaction is discussed in relation to the formation of more stable, secondary oxidation products that might be more useful markers of DNA damage.

8-Hydroxy-2'-Deoxyguanosine↗