Singlet molecular oxygen regulates vascular tone and blood pressure in inflammation.

Singlet molecular oxygen (1O2) has well-established roles in photosynthetic plants, bacteria and fungi1-3, but not in mammals. Chemically generated 1O2 oxidizes the amino acid tryptophan to precursors of a key metabolite called N-formylkynurenine4, whereas enzymatic oxidation of tryptophan to N-formylkynurenine is catalysed by a family of dioxygenases, including indoleamine 2,3-dioxygenase 15. Under inflammatory conditions, this haem-containing enzyme is expressed in arterial endothelial cells, where it contributes to the regulation of blood pressure6. However, whether indoleamine 2,3-dioxygenase 1 forms 1O2 and whether this contributes to blood pressure control have remained unknown. Here we show that arterial indoleamine 2,3-dioxygenase 1 regulates blood pressure via formation of 1O2. We observed that in the presence of hydrogen peroxide, the enzyme generates 1O2 and that this is associated with the stereoselective oxidation of L-tryptophan to a tricyclic hydroperoxide via a previously unrecognized oxidative activation of the dioxygenase activity. The tryptophan-derived hydroperoxide acts in vivo as a signalling molecule, inducing arterial relaxation and decreasing blood pressure; this activity is dependent on Cys42 of protein kinase G1α. Our findings demonstrate a pathophysiological role for 1O2 in mammals through formation of an amino acid-derived hydroperoxide that regulates vascular tone and blood pressure under inflammatory conditions.

Nicotinamide riboside Induced Energy Stress and Metabolic Reprogramming in BEAS-2B Cells.

Nicotinamide riboside (NR), a NAD+ precursor, has received attention due to several health benefits it has induced in experimental models. Studies in cultured cells, animals, and humans consistently show increased NAD+ availability after NR supplementation, which is considered the only mode of NR action that leads to health benefits. In the present study, we show that a persistently low NR concentration (1 µM) in the growth medium of BEAS-2B human cells, grown in a monolayer, induces energy stress, which precedes a cellular NAD+ increase after 192 h. NR concentrations greater than 1 µM under the specified conditions were cytotoxic in the 2D cell culture model, while all concentrations tested in the 3D cell culture model (BEAS-2B cell spheroids exposed to 1, 5, 10, and 50 µM NR) induced apoptosis. Shotgun proteomics revealed that NR modulated the abundance of proteins, agreeing with the observed effects on cellular energy metabolism and cell growth or survival. Energy stress may activate pathways that lead to health benefits such as cancer prevention. Accordingly, the premalignant 1198 cell line was more sensitive to NR cytotoxicity than the phenotypically normal parent BEAS-2B cell line. The role of a mild energy stress induced by low concentrations of NR in its beneficial effects deserves further investigation. On the other hand, strategies to increase the bioavailability of NR require attention to toxic effects that may arise.

Quantitative Analysis of Glutathione and Carnosine Adducts with 4-Hydroxy-2-nonenal in Muscle in a hSOD1G93A ALS Rat Model.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the dysfunction and death of motor neurons through multifactorial mechanisms that remain unclear. ALS has been recognized as a multisystemic disease, and the potential role of skeletal muscle in disease progression has been investigated. Reactive aldehydes formed as secondary lipid peroxidation products in the redox processes react with biomolecules, such as DNA, proteins, and amino acids, resulting in cytotoxic effects. 4-Hydroxy-2-nonenal (HNE) levels are elevated in the spinal cord motor neurons of ALS patients, and HNE-modified proteins have been identified in the spinal cord tissue of an ALS transgenic mice model, suggesting that reactive aldehydes can contribute to motor neuron degeneration in ALS. One biological pathway of aldehyde detoxification involves conjugation with glutathione (GSH) or carnosine (Car). Here, the detection and quantification of Car, GSH, GSSG (glutathione disulfide), and the corresponding adducts with HNE, Car-HNE, and GS-HNE, were performed in muscle and liver tissues of a hSOD1G93A ALS rat model by reverse-phase high-performance liquid chromatography coupled to electrospray ion trap tandem mass spectrometry in the selected reaction monitoring mode. A significant increase in the levels of GS-HNE and Car-HNE was observed in the muscle tissue of the end-stage ALS animals. Therefore, analyzing variations in the levels of these adducts in ALS animal tissue is crucial from a toxicological perspective and can contribute to the development of new therapeutic strategies.

Singlet Molecular Oxygen Reactions with Nucleic Acids, Lipids, and Proteins.

Singlet oxygen (1O2) is a biologically relevant reactive oxygen species capable of efficiently reacting with cellular constituents. The resulting oxidatively generated damage to nucleic acids, membrane unsaturated lipids, and protein components has been shown to be implicated in several diseases, including arthritis, cataracts, and skin cancer. Singlet oxygen may be endogenously produced, among various possibilities, by myeloperoxidase, an enzyme implicated in inflammation processes, and also efficiently in skin by the UVA component of solar radiation through photosensitization reactions. Emphasis is placed in this Review on the description of the main oxidation reactions initiated by 1O2 and the resulting modifications within key cellular targets, including guanine for nucleic acids, unsaturated lipids, and targeted amino acids. Most of these reactions give rise to peroxides and dioxetanes, whose formation has been rationalized in terms of [4+2] cycloaddition and 1,2-cycloaddition with dienes + olefins, respectively. The use of [18O]-labeled thermolabile endoperoxides as a source of [18O]-labeled 1O2 has been applied to study mechanistic aspects and preferential targets of 1O2 in biological systems. A relevant major topic deals with the search for the molecular signature of the 1O2 formation in targeted biomolecules within cells. It may be anticipated that [18O]-labeled 1O2 and labeled peroxides in association with sensitive mass spectrometric methods should constitute powerful tools for this purpose.

Comparing Data-Independent Acquisition and Parallel Reaction Monitoring in Their Abilities To Differentiate High-Density Lipoprotein Subclasses.

High-density lipoprotein (HDL) is a diverse group of particles with multiple cardioprotective functions. HDL proteome follows HDL particle complexity. Many proteins were described in HDL, but consistent quantification of HDL protein cargo is still a challenge. To address this issue, the aim of this work was to compare data-independent acquisition (DIA) and parallel reaction monitoring (PRM) methodologies in their abilities to differentiate HDL subclasses through their proteomes. To this end, we first evaluated the analytical performances of DIA and PRM using labeled peptides in pooled digested HDL as a biological matrix. Next, we compared the quantification capabilities of the two methodologies for 24 proteins found in HDL2 and HDL3 from 19 apparently healthy subjects. DIA and PRM exhibited comparable linearity, accuracy, and precision. Moreover, both methodologies worked equally well, differentiating HDL subclasses' proteomes with high precision. Our findings may help to understand HDL functional diversity.

Heck reaction synthesis of anthracene and naphthalene derivatives as traps and clean chemical sources of singlet molecular oxygen in biological systems.

Studies have previously shown that anthracene and naphthalene derivatives serve as compounds for trapping and chemically generating singlet molecular oxygen [O2(1Δg)], respectively. Simple and efficient synthetic routes to anthracene and naphthalene derivatives are needed, for improved capture and release of O2(1Δg) in cellular environments. Because of this need, we have synthesized a dihydroxypropyl amide naphthlene endoperoxide as a O2(1Δg) donor, as well as five anthracene derivatives as O2(1Δg) acceptor. The anthracene derivatives bear dihydroxypropyl amide, ester, and sulfonate ion end groups connected to 9,10-positions by way of unsaturated (vinyl) and saturated (ethyl) bridging groups. Heck reactions were found to yield these six compounds in easy-to-carry out 3-step reactions in yields of 50-76%. Preliminary results point to the potential of the anthracene compounds to serve as O2(1Δg) acceptors and would be amenable for future use in biological systems to expand the understanding of O2(1Δg) in biochemistry.

Ohr plays a central role in bacterial responses against fatty acid hydroperoxides and peroxynitrite.

Organic hydroperoxide resistance (Ohr) enzymes are unique Cys-based, lipoyl-dependent peroxidases. Here, we investigated the involvement of Ohr in bacterial responses toward distinct hydroperoxides. In silico results indicated that fatty acid (but not cholesterol) hydroperoxides docked well into the active site of Ohr from Xylella fastidiosa and were efficiently reduced by the recombinant enzyme as assessed by a lipoamide-lipoamide dehydrogenase-coupled assay. Indeed, the rate constants between Ohr and several fatty acid hydroperoxides were in the 107-108 M-1⋅s-1 range as determined by a competition assay developed here. Reduction of peroxynitrite by Ohr was also determined to be in the order of 107 M-1⋅s-1 at pH 7.4 through two independent competition assays. A similar trend was observed when studying the sensitivities of a ∆ohr mutant of Pseudomonas aeruginosa toward different hydroperoxides. Fatty acid hydroperoxides, which are readily solubilized by bacterial surfactants, killed the ∆ohr strain most efficiently. In contrast, both wild-type and mutant strains deficient for peroxiredoxins and glutathione peroxidases were equally sensitive to fatty acid hydroperoxides. Ohr also appeared to play a central role in the peroxynitrite response, because the ∆ohr mutant was more sensitive than wild type to 3-morpholinosydnonimine hydrochloride (SIN-1 , a peroxynitrite generator). In the case of H2O2 insult, cells treated with 3-amino-1,2,4-triazole (a catalase inhibitor) were the most sensitive. Furthermore, fatty acid hydroperoxide and SIN-1 both induced Ohr expression in the wild-type strain. In conclusion, Ohr plays a central role in modulating the levels of fatty acid hydroperoxides and peroxynitrite, both of which are involved in host-pathogen interactions.

Photosensitized Membrane Permeabilization Requires Contact-Dependent Reactions between Photosensitizer and Lipids.

Although the general mechanisms of lipid oxidation are known, the chemical steps through which photosensitizers and light permeabilize lipid membranes are still poorly understood. Herein we characterized the products of lipid photooxidation and their effects on lipid bilayers, also giving insight into their formation pathways. Our experimental system was designed to allow two phenothiazinium-based photosensitizers (methylene blue, MB, and DO15) to deliver the same amount of singlet oxygen molecules per second to 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine liposome membranes, but with a substantial difference in terms of the extent of direct physical contact with lipid double bonds; that is, DO15 has a 27-times higher colocalization with ω-9 lipid double bonds than MB. Under this condition, DO15 permeabilizes membranes at least 1 order of magnitude more efficiently than MB, a result that was also valid for liposomes made of polyunsaturated lipids. Quantification of reaction products uncovered a mixture of phospholipid hydroperoxides, alcohols, ketones, and aldehydes. Although both photosensitizers allowed the formation of hydroperoxides, the oxidized products that require direct reactions between photosensitizer and lipids were more prevalent in liposomes oxidized by DO15. Membrane permeabilization was always connected with the presence of lipid aldehydes, which cause a substantial decrease in the Gibbs free energy barrier for water permeation. Processes depending on direct contact between photosensitizers and lipids were revealed to be essential for the progress of lipid oxidation and consequently for aldehyde formation, providing a molecular-level explanation of why membrane binding correlates so well with the cell-killing efficiency of photosensitizers.

Oxidation of 1-N2-etheno-2'-deoxyguanosine by singlet molecular oxygen results in 2'-deoxyguanosine: a pathway to remove exocyclic DNA damage?

Exocyclic DNA adducts are considered as potential tools for the study of oxidative stress-related diseases, but an important aspect is their chemical reactivity towards oxidant species. We report here the oxidation of 1-N2-etheno-2'-deoxyguanosine (1,N2-εdGuo) by singlet molecular oxygen (1O2) generated by a non-ionic water-soluble endoperoxide [N,N'-di(2,3-dihydroxypropyl)-1,4-naphthalenedipropanamide endoperoxide (DHPNO2)] and its corresponding oxygen isotopically labeled [18O]-[N,N'-di(2,3-dihydroxypropyl)-1,4- naphthalenedipropanamide endoperoxide (DHPN18O2)], and by photosensitization with two different photosensitizers [methylene blue (MB) and Rose Bengal (RB)]. Products detection and characterization were achieved using high performance liquid chromatography (HPLC) coupled to ultraviolet and electrospray ionization (ESI) tandem mass spectrometry, and nuclear magnetic resonance (NMR) analyses. We found that dGuo is regenerated via reaction of 1O2 with the ε-linkage, and we propose a dioxetane as an intermediate, which cleaves and loses the aldehyde groups as formate residues, or alternatively, it generates a 1,2-ethanediol adduct. We also report herein the quenching rate constants of 1O2 by 1,N2-εdGuo and other etheno modified nucleosides. The rate constant (kt) values obtained for etheno nucleosides are comparable to the kt of dGuo. From these results, we suggest a possible role of 1O2 in the cleanup of etheno adducts by regenerating the normal base.

DNA Adduct Formation in the Lungs and Brain of Rats Exposed to Low Concentrations of [13C2]-Acetaldehyde.

Air pollution is a major environmental risk for human health. Acetaldehyde is present in tobacco smoke and vehicle exhaust. In this study, we show that [13C2]-acetaldehyde induces DNA modification with the formation of isotopically labeled 1, N2-propano-2'-deoxyguanosine adducts in the brain and lungs of rats exposed to concentrations of acetaldehyde found in the atmosphere of megacities. The adduct, with the addition of two molecules of isotopically labeled acetaldehyde [13C4]-1, N2-propano-dGuo, was detected in the lung and brain tissues of exposed rats by micro-HPLC/MS/MS. Structural confirmation of the products was unequivocally performed by nano-LC/ESI+-HRMS3 analyses. DNA modifications induced by acetaldehyde have been regarded as a key factor in the mechanism of mutagenesis and may be involved in the cancer risks associated with air pollution.

Genotoxic and epigenotoxic effects in mice exposed to concentrated ambient fine particulate matter (PM2.5) from São Paulo city, Brazil.

BACKGROUND: The Metropolitan Area of São Paulo has a unique composition of atmospheric pollutants, and positive correlations between exposure and the risk of diseases and mortality have been observed. Here we assessed the effects of ambient fine particulate matter (PM2.5) on genotoxic and global DNA methylation and hydroxymethylation changes, as well as the activities of antioxidant enzymes, in tissues of AJ mice exposed whole body to ambient air enriched in PM2.5, which was concentrated in a chamber near an avenue of intense traffic in São Paulo City, Brazil. RESULTS: Mice exposed to concentrated ambient PM2.5 (1 h daily, 3 months) were compared to in situ ambient air exposed mice as the study control. The concentrated PM2.5 exposed group presented increased levels of the oxidized nucleoside 8-oxo-7,8-dihydro-2'-deoxyguanosine in lung and kidney DNA and increased levels of the etheno adducts 1,N6-etheno-2'-deoxyadenosine and 1,N2-etheno-2'-deoxyguanosine in kidney and liver DNA, respectively. Apart from the genotoxic effects, the exposure to PM2.5 led to decreased levels of the epigenetic mark 5-hydroxymethylcytosine (5-hmC) in lung and liver DNA. Changes in lung, liver, and erythrocyte antioxidant enzyme activities were also observed. Decreased glutathione reductase and increased superoxide dismutase (SOD) activities were observed in the lungs, while the liver presented increased glutathione S-transferase and decreased SOD activities. An increase in SOD activity was also observed in erythrocytes. These changes are consistent with the induction of local and systemic oxidative stress. CONCLUSIONS: Mice exposed daily to PM2.5 at a concentration that mimics 24-h exposure to the mean concentration found in ambient air presented, after 3 months, increased levels of DNA lesions related to the occurrence of oxidative stress in the lungs, liver, and kidney, in parallel to decreased global levels of 5-hmC in lung and liver DNA. Genetic and epigenetic alterations induced by pollutants may affect the genes committed to cell cycle control, apoptosis, and cell differentiation, increasing the chance of cancer development, which merits further investigation.

Experimental and DFT Computational Insight into Nitrosamine Photochemistry-Oxygen Matters.

A nitrosamine photooxidation reaction is shown to generate a peroxy intermediate by experimental physical-organic methods. The irradiation of phenyl and methyl-substituted nitrosamines in the presence of isotopically labeled 18-oxygen revealed that an O atom was trapped from a peroxy intermediate to trimethylphosphite or triphenylphosphine, or by nitrosamine itself, forming two moles of nitramine. The unstable peroxy intermediate can be trapped at low temperature in postphotolyzed solution in the dark. Chemiluminescence was also observed upon thermal decomposition of the peroxy intermediate, that is, when a postphotolysis low-temperature solution is brought up to room temperature. A DFT study provides tentative information for cyclic nitrogen peroxide species on the reaction surface.

Singlet molecular oxygen: Düsseldorf - São Paulo, the Brazilian connection.

Inspired by Helmut Sies we continue the development of suitable chemical generators of (1)O2 based on the thermodissociation of naphthalene endoperoxide derivatives. The present manuscript focuses on how the use of [(18)O]-labeled endoperoxides and hydroperoxides can be applied to study mechanistic aspects related to the generation of singlet molecular oxygen and its reactions in biological systems. The peroxidation reactions of the main cellular targets including unsaturated lipids, proteins and nucleic acids have received major attention during the last three decades. Emphasis is placed in this manuscript on the description of the synthesis and the main use of [(18)O]-labeled compounds, and especially of peroxides and (1)O2, for tracer elucidation of reaction mechanisms.

Cytochrome c reacts with cholesterol hydroperoxides to produce lipid- and protein-derived radicals.

Lipid peroxidation is a well-known process that has been implicated in many diseases. Recent evidence has shown that mitochondrial cholesterol levels are increased under specific conditions, making it an important target for peroxidation inside the mitochondria. Cholesterol peroxidation generates, as primary products, several hydroperoxides (ChOOH), which can react with transition metals and metalloproteins. In this sense, cytochrome c (CYTC), a heme protein largely found in the mitochondria, becomes a candidate to react with ChOOH. Using CYTC associated with SDS micelles to mimic mitochondrial conditions, we show that ChOOH induces dose-dependent CYTC Soret band bleaching, indicating that it is using ChOOH as a substrate. This reaction leads to protein oligomerization, suggesting the formation of a protein radical that, subsequently, recombines, giving dimers, trimers, and tetramers. EPR experiments confirmed the production of carbon-centered radicals from both protein and lipid in the presence of ChOOH. Similar results were obtained with linoleic acid hydroperoxides (LAOOH). In addition, replacing SDS micelles by cardiolipin-containing liposomes as the mitochondrial mimetic led to similar results with either ChOOH or LAOOH. Importantly, kinetic experiments show that CYTC bleaching is faster with ChOOH than with H2O2, suggesting that these hydroperoxides could be relevant substrates for CYTC peroxidase-like activity in biological media. Altogether, these results show that CYTC induces homolytic cleavage of lipid-derived hydroperoxides, producing lipid and protein radicals.

Glutathione modifies the oxidation products of 2'-deoxyguanosine by singlet molecular oxygen.

The oxidation of the free nucleoside 2'-deoxyguanosine (dGuo) by singlet molecular oxygen ((1)O2) has been studied over the three last decades due to the major role of DNA oxidation products in process such as ageing, mutation and carcinogenesis. In the present work we investigated the dGuo oxidation by (1)O2 in the presence of the important low molecular antioxidant, glutathione, in its reduced (GSH) and oxidized (GSSG) forms. There were applied different conditions of concentration, pH, time of incubation, and the use of a [(18)O]-labeled thermolabile endoperoxide naphthalene derivative as a source of [(18)O]-labeled (1)O2. Data was obtained through high performance liquid chromatography (HPLC) and HPLC coupled to micrOTOF Q-II analysis of the main oxidation products: the diastereomers of spiroiminodihydantoin-2'-deoxyribonucleosides (dSp) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo). An intriguing result was that 8-oxodGuo levels increased by 100 fold when dGuo was oxidized by (1)O2 in the presence of GSH and by 2 fold in the presence of GSSG, while dSp levels dropped to zero for both conditions. All data from dGuo, 8-oxodGuo and dSp quantification together with the analysis of residual GSH/GSSG content in each sample strongly suggest that glutathione modifies the mechanism of dGuo oxidation by (1)O2 by disfavoring the pathway of dSp formation.

Chemical Characterization of Urate Hydroperoxide, A Pro-oxidant Intermediate Generated by Urate Oxidation in Inflammatory and Photoinduced Processes.

Urate hydroperoxide is a strong oxidant generated by the combination of urate free radical and superoxide. The formation of urate hydroperoxide as an intermediate in urate oxidation is potentially responsible for the pro-oxidant effects of urate in inflammatory disorders, protein degradation, and food decomposition. To understand the molecular mechanisms that sustain the harmful effects of urate in inflammatory and oxidative stress related conditions, we report a detailed structural characterization and reactivity of urate hydroperoxide toward biomolecules. Urate hydroperoxide was synthesized by photo-oxidation and by a myeloperoxidase/hydrogen peroxide/superoxide system. Multiple reaction monitoring (MRM) and MS(3) ion fragmentation revealed that urate hydroperoxide from both sources has the same chemical structure. Urate hydroperoxide has a maximum absorption at 308 nm, ε308nm = 6.54 ± 0.38 × 10(3) M(-1) cm(-1). This peroxide decays spontaneously with a rate constant of k = 2.80 ± 0.18 × 10(-4) s(-1) and a half-life of 41 min at 22 °C. Urate hydroperoxide undergoes electrochemical reduction at potential values less negative than -0.5 V (versus Ag/AgCl). When incubated with taurine, histidine, tryptophan, lysine, methionine, cysteine, or glutathione, urate hydroperoxide reacted only with methionine, cysteine, and glutathione. The oxidation of these molecules occurred by a two-electron mechanism, generating the alcohol, hydroxyisourate. No adduct between cysteine or glutathione and urate hydroperoxide was detected. The second-order rate constant for the oxidation of glutathione by urate hydroperoxide was 13.7 ± 0.8 M(-1) s(-1). In conclusion, the oxidation of sulfur-containing biomolecules by urate hydroperoxide is likely to be a mechanism by which the pro-oxidant and damaging effects of urate are mediated in inflammatory and photo-oxidizing processes.

Mechanism of Photochemical O-Atom Exchange in Nitrosamines with Molecular Oxygen.

The detection of an oxygen-atom photoexchange process of N-nitrosamines is reported. The photolysis of four nitrosamines (N-nitrosodiphenylamine 1, N-nitroso-N-methylaniline 2, N-butyl-N-(4-hydroxybutyl)nitrosamine 3, and N-nitrosodiethylamine 4) with ultraviolet light was examined in an (18)O2-enriched atmosphere in solution. HPLC/MS and HPLC-MS/MS data show that (18)O-labeled nitrosamines were generated for 1 and 2. In contrast, nitrosamines 3 and 4 do not exchange the (18)O label and instead decomposed to amines and/or imines under the conditions. For 1 and 2, the (18)O atom was found not to be introduced by moisture or by singlet oxygen [(18)((1)O2 (1)Δg)] produced thermally by (18)O-(18)O labeled endoperoxide of N,N'-di(2,3-hydroxypropyl)-1,4-naphthalene dipropanamide (DHPN(18)O2) or by visible-light sensitization. A density functional theory study of the structures and energetics of peroxy intermediates arising from reaction of nitrosamines with O2 is also presented. A reversible head-to-tail dimerization of the O-nitrooxide to the 1,2,3,5,6,7-hexaoxadiazocane (30 kcal/mol barrier) with extrusion of O═(18)O accounts for exchange of the oxygen atom label. The unimolecular cyclization of O-nitrooxide to 1,2,3,4-trioxazetidine (46 kcal/mol barrier) followed by a retro [2 + 2] reaction is an alternative, but higher energy process. Both pathways would require the photoexcitation of the nitrooxide.

Lipid hydroperoxides as a source of singlet molecular oxygen.

Lipid hydroperoxides (LOOH) are formed in biological system by enzymatic and non-enzymatic pathways. These hydroperoxides exerts multiple damaging effects on cellular macromolecules and are also important regulators of cellular processes. Several classes of hydroperoxides including fatty acid, phospholipid, cholesterol and cholesteryl ester hydroperoxides have been detected and characterized both in vitro and in vivo. Although cells are normally endowed with enzymatic defenses capable to reduce LOOH to less reactive hydroxides, LOOH may accumulate in several pathological conditions and attention has been focused on elucidating their pathophysiological role. In the last years we have demonstrated the generation of singlet molecular oxygen (O2 (1)Δg or (1)O2) in several reactions involving LOOH. The generation of (1)O2 was directly evidenced by spectroscopic detection and characterization of its light emission at 1,270 nm. Moreover, using 18-oxygen labeled hydroperoxides (L(18)O(18)OH) we could detect the formation of (18)O-labeled (1)O2 by chemical trapping with anthracene derivatives followed by detection of the corresponding labeled endoperoxides by HPLC coupled to tandem mass spectrometry. The experimental evidences indicate that (1)O2 is generated at a yield close to 10 % by the Russell mechanism from LOOH, either free or in membranes, in the presence of biologically relevant oxidants, such as metal ions, peroxynitrite, HOCl and cytochrome c.

Effects of the melanin precursor 5,6-dihydroxy-indole-2-carboxylic acid (DHICA) on DNA damage and repair in the presence of reactive oxygen species.

Eumelanin is a heterogeneous polymer composed of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and 5,6-dihydroxyindole (DHI). Studies have shown that DHICA promotes single strand breaks in plasmid DNA exposed to ultraviolet B radiation (UVB, 313 nm) and in DNA from human keratinocytes exposed to ultraviolet A radiation (UVA, 340-400 nm). Singlet molecular oxygen ((1)O2) is the main reactive species formed by UVA radiation on the skin. In this context, we now report that DHICA can cause single strand breaks in plasmid DNA even in the absence of light radiation. Interestingly, when DHICA was pre-oxidized by (1)O2, it lost this harmful capacity. It was also found that DHICA could interact with DNA, disturbing Fpg activity and decreasing its recognition of lesions by ∼50%. Additionally, the free nucleoside deoxyguanosine (dGuo) was used to evaluate whether DHICA would interfere with the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) and spiroiminodihydantoin (dSp) by (1)O2 or with the formation of 8-oxodGuo by hydroxyl radical (OH). We observed that when dGuo was oxidized by (1)O2 in the presence of DHICA, 8-oxodGuo formation was increased. However, when dGuo was oxidized by OH in the presence of DHICA, 8-oxodGuo levels were lower than in the absence of the precursor. Overall, our data reveal an important role for this eumelanin precursor in both the promotion and the protection of DNA damage and imply that it can impair DNA repair.

The carbonylation and covalent dimerization of human superoxide dismutase 1 caused by its bicarbonate-dependent peroxidase activity is inhibited by the radical scavenger tempol.

Tempol (4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl) reduces tissue injury in animal models of various diseases via mechanisms that are not completely understood. Recently, we reported that high doses of tempol moderately increased survival in a rat model of ALS (amyotrophic lateral sclerosis) while decreasing the levels of oxidized hSOD1 (human Cu,Zn-superoxide dismutase) in spinal cord tissues. To better understand such a protective effect in vivo, we studied the effects of tempol on hSOD1 oxidation in vitro. The chosen oxidizing system was the bicarbonate-dependent peroxidase activity of hSOD1 that consumes H2O2 to produce carbonate radical, which oxidizes the enzyme. Most of the experiments were performed with 30 µM hSOD1, 25 mM bicarbonate, 1 mM H2O2, 0.1 mM DTPA (diethylenetriaminepenta-acetic acid) and 50 mM phosphate buffer at a final pH of 7.4. The results showed that tempol (5-75 µM) does not inhibit hSOD1 turnover, but decreases its resulting oxidation to carbonylated and covalently dimerized forms. Tempol acted by scavenging the carbonate radical produced and by recombining with hSOD1-derived radicals. As a result, tempol was consumed nearly stoichiometrically with hSOD1 monomers. MS analyses of turned-over hSOD1 and of a related peptide oxidized by the carbonate radical indicated the formation of a relatively unstable adduct between tempol and hSOD1-Trp32•. Tempol consumption by the bicarbonate-dependent peroxidase activity of hSOD1 may be one of the reasons why high doses of tempol were required to afford protection in an ALS rat model. Overall, the results of the present study confirm that tempol can protect against protein oxidation and the ensuing consequences.