Plasma oxylipin profiling by high resolution mass spectrometry reveal signatures of inflammation and hypermetabolism in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive loss of motor neurons, systemic hypermetabolism, and inflammation. In this context, oxylipins have been investigated as signaling molecules linked to neurodegeneration, although their specific role in ALS remains unclear. Importantly, most methods focused on oxylipin analysis are based on low-resolution mass spectrometry, which usually confers high sensitivity, but not great accuracy for molecular characterization, as provided by high-resolution MS (HRMS). Here, we established an ultra-high performance liquid chromatography HRMS (LC-HRMS) method for simultaneous analysis of 126 oxylipins in plasma. Intra- and inter-day method validation showed high sensitivity (0.3-25 pg), accuracy and precision for more than 90% of quality controls. This method was applied in plasma of ALS rats overexpressing the mutant human Cu/Zn-superoxide dismutase gene (SOD1-G93A) at asymptomatic (ALS 70 days old) and symptomatic stages (ALS 120 days old), and their respective age-matched wild type controls. From the 56 oxylipins identified in plasma, 17 species were significantly altered. Remarkably, most of oxylipins linked to inflammation and oxidative stress derived from arachidonic acid (AA), like prostaglandins and mono-hydroxides, were increased in ALS 120 d rats. In addition, ketones derived from AA and linoleic acid (LA) were increased in both WT 120 d and ALS 120 d groups, supporting that age also modulates oxylipin metabolism in plasma. Interestingly, the LA-derived diols involved in fatty acid uptake and β-oxidation, 9(10)-DiHOME and 12(13)-DiHOME, were decreased in ALS 120 d rats and showed significant synergic effects between age and disease factors. In summary, we validated a high-throughput LC-HRMS method for oxylipin analysis and provided a comprehensive overview of plasma oxylipins involved in ALS disease progression. Noteworthy, the oxylipins altered in plasma have potential to be investigated as biomarkers for inflammation and hypermetabolism in ALS.

Detection of DNA Adduct Formation in Rat Lungs by a Micro-HPLC/MS/MS Approach

Aldehydes are abundantly present in tobacco smoke and in urban air pollution and are endogenously generated as products of the lipid peroxidation process. These molecules can react with DNA bases forming mutagenic exocyclic adducts, which have been used as biomarkers of aldehyde exposure and as potential tools for the study of inflammation, metal storage diseases, neurodegenerative disorders, and cancer. High-performance liquid chromatography-tandem mass spectrometry (HPLC/MS/MS) provides a highly precise, specific and ultrasensitive method for the detection of exocyclic DNA adducts. Here we present and describe a validated micro-HPLC-Electro Spray Ionization (ESI)-MS/MS method for the quantification of 1,N²-propanodGuo, an adduct produced following the reaction between 2'-deoxyguanosine and acetaldehyde or crotonaldehyde.

Lipid aldehyde hydrophobicity affects apo-SOD1 modification and aggregation

Unsaturated lipids are oxidized by reactive oxygen species and enzymes, leading to the increased formation of lipid hydroperoxides and several electrophilic products. Lipid-derived electrophiles can modify macromolecules, such as proteins, resulting in the loss of function and/or aggregation. The accumulation of Cu,Zn-superoxide dismutase (SOD1) aggregates has been associated with familial cases of amyotrophic lateral sclerosis (ALS). The protein aggregation mechanisms in motor neurons remain unclear, although recent studies have shown that lipids and oxidized lipid derivatives may play roles in this process. Here, we aimed to compare the effects of different lipid aldehydes on the induction of SOD1 modifications and aggregation, in vitro. Human recombinant apo-SOD1 was incubated with 4-hydroxy-2-hexenal (HHE), 4-hydroxy-2-nonenal (HNE), 2-hexen-1-al (HEX), 2,4-nonadienal (NON), 2,4-decadienal (DEC), or secosterol aldehydes (SECO-A or SECO-B). High-molecular-weight apo-SOD1 aggregates dramatically increased in the presence of highly hydrophobic aldehydes (LogP_calc > 3). Notably, several Lys residues were modified by exposure to all aldehydes. The observed modifications were primarily observed on Lys residues located near the dimer interface (K3 and K9) and at the electrostatic loop (K122, K128, and K136). Moreover, HHE and HNE induced extensive apo-SOD1 modifications, by forming Schiff bases or Michael adducts with Lys, His, and Cys residues. However, these aldehydes were unable to induce large protein aggregates. Overall, our data shed light on the importance of lipid aldehyde hydrophobicity on the induction of apo-SOD1 aggregation and identified preferential sites of lipid aldehyde-induced modifications.

Generation of Singlet Molecular Oxygen by Lipid Hydroperoxides and Nitronium Ion†

Singlet molecular oxygen is a reactive species involved in biological oxidative processes. The major cellular targets of singlet molecular oxygen are unsaturated fatty acids in the membrane, as well as nucleic acids and proteins. The aim of this study was to investigate whether lipids and commercial hydroperoxides generate singlet molecular oxygen, in presence of nitronium and activated nitronium ion. For this purpose, monomol light emitted in the near-infrared region (λ = 1270 nm) was used to monitor singlet molecular oxygen decay in different solvents, with different hydroperoxides and in the presence of azide. Direct measurements of the singlet molecular oxygen spectrum at 1270 nm recorded during the reaction between lipids and commercial hydroperoxides and nitronium ions unequivocally demonstrated the formation of this excited species.

Contribution of GO System Glycosylases to Mutation Prevention in Caulobacter crescentus

8-oxo-7,8-dihydroguanine, commonly referred to as 8-oxoG, is considered one of the most predominant oxidative lesions formed in DNA. Due to its ability to pair with adenines in its syn configuration, this lesion has a strong mutagenic potential in both eukaryotes and prokaryotes. Escherichia coli cells are endowed with the GO system, which protects them from the mutagenic properties of this lesion when formed both in cellular DNA and the nucleotide pool. MutY and MutM (Fpg) DNA glycosylases are crucial components of the GO system. A strong mutator phenotype of the Escherichia coli mutM mutY double mutant underscores the importance of 8-oxoG repair for genomic stability. Here, we report that in Caulobacter crescentus, a widely studied alpha-proteobacterium with a GC-rich genome, the combined lack of MutM and MutY glycosylases produces a more modest mutator phenotype when compared to E. coli. Genetic analysis indicates that other glycosylases and other repair pathways do not act synergistically with the GO system for spontaneous mutation prevention. We also show that there is not a statistically significant difference in the spontaneous levels 8-oxodGuo in E. coli and C. crescentus, suggesting that other yet to be identified differences in repair or replication probably account for the differential importance of the GO system between these two species. Environ. Mol. Mutagen. 61:246-255, 2020. © 2019 Wiley Periodicals, Inc.

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

Our study shows that new anthracene and naphthalene derivatives function as compounds for trapping and chemically generating singlet molecular oxygen [O₂(¹Δ_g)], respectively. The syntheses of these derivatives are described, as well as some localization testing in cells.

Singlet oxygen-induced protein aggregation: Lysozyme crosslink formation and nLC-MS/MS characterization

Singlet molecular oxygen (¹ O₂ ) has been associated with a number of physiological processes. Despite the recognized importance of ¹ O₂ -mediated protein modifications, little is known about the role of this oxidant in crosslink formation and protein aggregation. Thus, using lysozyme as a model, the present study sought to investigate the involvement of ¹ O₂ in crosslink formation. Lysozyme was photochemically oxidized in the presence of rose bengal or chemically oxidized using [¹⁸ O]-labeled ¹ O₂ released from thermolabile endoperoxides. It was concluded that both ¹ O₂ generating systems induce lysozyme crosslinking and aggregation. Using SDS-PAGE and nano-scale liquid chromatography coupled to electrospray ionization mass spectrometry, the results clearly demonstrated that ¹ O₂ is directly involved in the formation of covalent crosslinks involving the amino acids histidine, lysine, and tryptophan.

Where do we aspire to publish? A position paper on scientific communication in biochemistry and molecular biology

The scientific publication landscape is changing quickly, with an enormous increase in options and models. Articles can be published in a complex variety of journals that differ in their presentation format (online-only or in-print), editorial organizations that maintain them (commercial and/or society-based), editorial handling (academic or professional editors), editorial board composition (academic or professional), payment options to cover editorial costs (open access or pay-to-read), indexation, visibility, branding, and other aspects. Additionally, online submissions of non-revised versions of manuscripts prior to seeking publication in a peer-reviewed journal (a practice known as pre-printing) are a growing trend in biological sciences. In this changing landscape, researchers in biochemistry and molecular biology must re-think their priorities in terms of scientific output dissemination. The evaluation processes and institutional funding for scientific publications should also be revised accordingly. This article presents the results of discussions within the Department of Biochemistry, University of São Paulo, on this subject.

Alterations in lipid metabolism of spinal cord linked to amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is characterized by progressive loss of upper and lower motor neurons leading to muscle paralysis and death. While a link between dysregulated lipid metabolism and ALS has been proposed, lipidome alterations involved in disease progression are still understudied. Using a rodent model of ALS overexpressing mutant human Cu/Zn-superoxide dismutase gene (SOD1-G93A), we performed a comparative lipidomic analysis in motor cortex and spinal cord tissues of SOD1-G93A and WT rats at asymptomatic (~70 days) and symptomatic stages (~120 days). Interestingly, lipidome alterations in motor cortex were mostly related to age than ALS. In contrast, drastic changes were observed in spinal cord of SOD1-G93A 120d group, including decreased levels of cardiolipin and a 6-fold increase in several cholesteryl esters linked to polyunsaturated fatty acids. Consistent with previous studies, our findings suggest abnormal mitochondria in motor neurons and lipid droplets accumulation in aberrant astrocytes. Although the mechanism leading to cholesteryl esters accumulation remains to be established, we postulate a hypothetical model based on neuroprotection of polyunsaturated fatty acids into lipid droplets in response to increased oxidative stress. Implicated in the pathology of other neurodegenerative diseases, cholesteryl esters appear as attractive targets for further investigations.

The molecular structure of β-alanine is resistant to sterilising doses of gamma radiation

β-alanine is the rate-limiting point for the endogenous synthesis of carnosine in skeletal muscle. Carnosine has a wide range of implications for health, normal function and exercise performance. Whilst the physiological relevance of carnosine to different tissues remains enigmatic, β-alanine administration is a useful strategy to investigate the physiological roles of carnosine in humans. Intravenous administration of β-alanine is an interesting approach to study carnosine metabolism. However, sterilisation is mandatory due to the nature of the administration route. We evaluated whether sterilising doses of gamma radiation damages the molecular structure and leads to the loss of functional characteristics of β-alanine. Pure β-alanine was sterilised by gamma radiation in sealed glass vials using a 60Co multipurpose irradiator at a dose rate of 8.5 kGy.hour-1 totalising 10, 20, 25 30 and 40 kGy. The molecular integrity was assessed by X-ray Diffraction and changes in content were determined by High Performance Liquid Chromatography (UV-HPLC) and Triple Quadrupole Mass Spectrometer (HPLC/MS-MS). Sterility assurance was evaluated by inoculation assay. To examine whether functional properties were preserved, β-alanine was infused in one participant, who rated the level of paraesthesia on the skin using a 0-3 scale. Urinary β-alanine was quantified before and 24-h following β-alanine infusion using HPLC-ESI+-MS/MS. Irradiation resulted in no change in the crystal structure of β-alanine, no degradation, and no new peaks were identified in the dose range assayed. The inoculation assay showed the absence of viable microorganisms in all β-alanine samples, including those that did not undergo irradiation. Intravenous infusion of β-alanine resulted in paraesthesia and it detected in the urine as per normal. We conclude that gamma radiation is a suitable technique for the sterilisation of β-alanine. It does not lead to degradation, damage to the β-alanine structure, content or loss of function within the evaluated irradiation conditions.

Iron Deficiency Generates Oxidative Stress and Activation of the SOS Response in Caulobacter crescentus

In C. crescentus, iron metabolism is mainly controlled by the transcription factor Fur (ferric uptake regulator). Iron-bound Fur represses genes related to iron uptake and can directly activate the expression of genes for iron-containing proteins. In this work, we used total RNA sequencing (RNA-seq) of wild type C. crescentus growing in minimal medium under iron limitation and a fur mutant strain to expand the known Fur regulon, and to identify novel iron-regulated genes. The RNA-seq of cultures treated with the iron chelator 2-2-dypiridyl (DP) allowed identifying 256 upregulated genes and 236 downregulated genes, being 176 and 204 newly identified, respectively. Sixteen transcription factors and seven sRNAs were upregulated in iron limitation, suggesting that the response to low iron triggers a complex regulatory network. Notably, lexA along with most of its target genes were upregulated, suggesting that DP treatment caused DNA damage, and the SOS DNA repair response was activated in a RecA-dependent manner, as confirmed by RT-qPCR. Fluorescence microscopy assays using an oxidation-sensitive dye showed that wild type cells in iron limitation and the fur mutant were under endogenous oxidative stress, and a direct measurement of cellular H₂O₂ showed that cells in iron-limited media present a higher amount of endogenous H₂O₂. A mutagenesis assay using the rpoB gene as a reporter showed that iron limitation led to an increase in the mutagenesis rate. These results showed that iron deficiency causes C. crescentus cells to suffer oxidative stress and to activate the SOS response, indicating an increase in DNA damage.

Exercise and β-alanine supplementation on carnosine-acrolein adduct in skeletal muscle

Previous studies have demonstrated that exercise results in reactive aldehyde production and that β-alanine supplementation increases carnosine content in skeletal muscle. However, little is known about the influence exercise and β-alanine supplementation have on the formation of carnosine-aldehydes. The goal of the present study was to monitor the formation of carnosine-aldehyde adducts, following high-intensity intermittent exercise, before and after β-alanine supplementation. Vastus lateralis biopsy samples were taken from 14 cyclists, before and after a 28 day β-alanine supplementation, following 4 bouts of a 30 s all-out cycling test, and carnosine and CAR-aldehyde adducts [carnosine-acrolein, CAR-ACR (m/z 303), carnosine-4-hydroxy-2-hexenal, CAR-HHE (m/z 341) and carnosine-4-hydroxy-2-nonenal, CAR-HNE (m/z 383)] were quantified by HPLC-MS/MS. β-alanine supplementation increased muscle carnosine content by ~50% (p = 0.0001 vs. Pre-Supplementation). Interestingly, there was a significant increase in post-exercise CAR-ACR content following β-alanine supplementation (p < 0.001 vs. post-exercise before supplementation), whereas neither exercise alone nor supplementation alone increased CAR-ACR formation. These results suggest that carnosine functions as an acrolein-scavenger in skeletal muscle. Such a role would be relevant to the detoxification of this aldehyde formed during exercise, and appears to be enhanced by β-alanine supplementation. These novel findings not only have the potential of directly benefiting athletes who engage in intensive training regimens, but will also allow researchers to explore the role of muscle carnosine in detoxifying reactive aldehydes in diseases characterized by abnormal oxidative stress.

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Lipid peroxidation generates electrophilic reactive aldehydes.

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β-Alanine supplementation increases muscle carnosine content in skeletal muscle.

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The carnosine-acrolein levels were higher in muscle following β-alanine supplementation in post-exercise.

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This acrolein-scavenger role for muscle carnosine may contribute to its ergogenic and therapeutic effects.

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.

Lysozyme oxidation by singlet molecular oxygen: Peptide characterization using [18 O]-labeling oxygen and nLC-MS/MS

Singlet molecular oxygen (¹ O₂ ) is generated in biological systems and reacts with different biomolecules. Proteins are a major target for ¹ O₂ , and His, Tyr, Met, Cys, and Trp are oxidized at physiological pH. In the present study, the modification of lysozyme protein by ¹ O₂ was investigated using mass spectrometry approaches. The experimental findings showed methionine, histidine, and tryptophan oxidation. The experiments were achieved using [¹⁸ O]-labeled ¹ O₂ released from thermolabile endoperoxides in association with nano-scale liquid chromatography coupled to electrospray ionization mass spectrometry. The structural characterization by nLC-MS/MS of the amino acids in the tryptic peptides of the proteins showed addition of [¹⁸ O]-labeling atoms in different amino acids.

Caloric restriction protects livers from ischemia/reperfusion damage by preventing Ca2+-induced mitochondrial permeability transition

Caloric restriction (CR) promotes lifespan extension and protects against many pathological conditions, including ischemia/reperfusion injury to the brain, heart and kidney. In the liver, ischemia/reperfusion damage is related to excessive mitochondrial Ca²⁺ accumulation, leading to the mitochondrial permeability transition. Indeed, liver mitochondria isolated from animals maintained on CR for 4 months were protected against permeability transition and capable of taking up Ca²⁺ at faster rates and in larger quantities. These changes were not related to modifications in mitochondrial respiratory activity, but rather to a higher proportion of ATP relative to ADP in CR liver mitochondria. Accordingly, both depletion of mitochondrial adenine nucleotides and loading mitochondria with exogenous ATP abolished the differences between CR and ad libitum (AL) fed groups. The prevention against permeability transition promoted by CR strongly protected against in vivo liver damage induced by ischemia/reperfusion. Overall, our results show that CR strongly protects the liver against ischemia/reperfusion and uncover a mechanism for this protection, through a yet undescribed diet-induced change in liver mitochondrial Ca²⁺ handling related to elevated intramitochondrial ATP.

Melanin photosensitization and the effect of visible light on epithelial cells

Protecting human skin from sun exposure is a complex issue that involves unclear aspects of the interaction between light and tissue. A persistent misconception is that visible light is safe for the skin, although several lines of evidence suggest otherwise. Here, we show that visible light can damage melanocytes through melanin photosensitization and singlet oxygen (¹O₂) generation, thus decreasing cell viability, increasing membrane permeability, and causing both DNA photo-oxidation and necro-apoptotic cell death. UVA (355 nm) and visible (532 nm) light photosensitize ¹O₂ with similar yields, and pheomelanin is more efficient than eumelanin at generating ¹O₂ and resisting photobleaching. Although melanin can protect against the cellular damage induced by UVB, exposure to visible light leads to pre-mutagenic DNA lesions (i.e., Fpg- and Endo III-sensitive modifications); these DNA lesions may be mutagenic and may cause photoaging, as well as other health problems, such as skin cancer.

Quantification of DNA adducts in lungs, liver and brain of rats exposed to acetaldehyde

Air pollution is a major risk for human health. Acetaldehyde is an environmental pollutant present in tobacco smoke, vehicle exhaust and several food products. Formation of DNA adducts has been regarded as a critical factor in the mechanisms of acetaldehyde mutagenicity and carcinogenesis. Acetaldehyde reacts with 2'-deoxyguanosine in DNA to primarily form N(2)-ethylidene-2'-deoxyguanosine (N(2)-ethylidene-dGuo). The subsequent reaction of N(2)-ethylidene-dGuo with another molecule of acetaldehyde gives rise to 1,N(2)-propano-2´-deoxyguanosine (1,N(2)-propanodGuo). In this study, on-line reverse-phase high-performance liquid chromatography (HPLC) separation with tandem mass spectrometry detection was utilized for the accurate quantification of 1,N(2)-propanodGuo and 1,N(2)-etheno-2'-deoxyguanosine (1,N(2)-edGuo) in tissues of rats exposed to 12 ppb, 33 ppb and 96 ppb acetaldehyde in atmospheric air for 50 days. A significant increase in the levels of 1,N(2)-propanodGuo was observed in lung tissues of rats exposed to 12 ppb (7.8/10(8) dGuo); 33 ppb (8.9/10(8) dGuo) and 96 ppb (11.6/10(8) dGuo) compared to controls (4.2/10(8) dGuo). For comparative purposes, the levels of 1,N(2)-etheno-2'-deoxyguanosine (1,N(2)-edGuo), which is produced from a,b-unsaturated aldehydes formed during the lipid peroxidation process were also measured. Elevated levels of 1,N(2)-edGuo were observed only in lung tissues of animals exposed to 96 ppb acetaldehyde. 1,N(2)-propanodGuo also differed quantitatively in liver but not in brain. The monitoring of 1,N(2)-propanodGuo levels in tissues provides important information on acetaldehyde genotoxicity and may contribute to the elucidation of the mechanisms associated with acetaldehyde exposure and cancer risk. Supported byFAPESP:2011/10048-5, CAPES, INCT Redoxoma:573530/2008-4,NAP Redoxoma: 2011.1.9352.1.8, CEPID Redoxoma:2013/07937-8.

Singlet molecular oxygen generated in dark biological process

Ultraweak chemiluminescence arising from biomolecules oxidation has been attributed to the radiative deactivation of singlet molecular oxygen [(1)O2] and electronically excited triplet carbonyl products involving dioxetane intermediates. As examples, we will discuss the generation of (1)O2 from lipid hydroperoxides, which involves a cyclic mechanism from a linear tetraoxide intermediate. The generation of (1)O2 in aqueous solution via energy transfer from the excited triplet acetone arising from the thermodecomposition of dioxetane a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source, will also be discussed. The approach used to unequivocally demonstrate the generation of (1)O2 in these reactions is the use of (18)O-labeled hydroperoxide / triplet dioxygen ((18)[(3)O2]), the detection of labeled compounds by HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) and the direct spectroscopic detection and characterization of (1)O2 light emission. Characteristic light emission at 1,270nm, corresponding to the singlet delta state monomolecular decay was observed. Using(18)[(3)O2], we observed the formation of (18)O-labeled (1)O2 ((18)[(1)O2]) by the chemical trapping of (18)[(1)O2]with the anthracene-9,10-diyldiethane-2,1-diyl disulfate disodium salt (EAS) and detected the corresponding (18)O-labeled EAS endoperoxide usingHPLC-MS/MS. The combined use of the thermolysis of a water-soluble naphthalene endoperoxide as a generator of (18)O labeled (1)O2 and the sensitivity of HPLC-MS/MS allowed the study of (1)O2reactivity toward biomolecules. Photoemission properties and chemical trapping clearly demonstrate that the production of hydroperoxide and excited carbonyls generates (18)[(1)O2], and points to the involvement of (1)O2 in physiological and pathophysiological mechanism. Supported by FAPESP (2012/12663-1), CAPES, INCT Redoxoma (FAPESP/CNPq/CAPES; 573530/2008-4), NAP Redoxoma (PRPUSP; 2011.1.9352.1.8), CEPID Redoxoma (FAPESP; 2013/07937-8).

Excited singlet molecular O₂(¹Δg) is generated enzymatically from excited carbonyls in the dark

In mammalian tissues, ultraweak chemiluminescence arising from biomolecule oxidation has been attributed to the radiative deactivation of singlet molecular oxygen [O2 ((1)Δg)] and electronically excited triplet carbonyl products involving dioxetane intermediates. Herein, we describe evidence of the generation of O2 ((1)Δg) in aqueous solution via energy transfer from excited triplet acetone. This involves thermolysis of 3,3,4,4-tetramethyl-1,2-dioxetane, a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source. Both sources of excited carbonyls showed characteristic light emission at 1,270 nm, directly indicative of the monomolecular decay of O2 ((1)Δg). Indirect analysis of O2 ((1)Δg) by electron paramagnetic resonance using the chemical trap 2,2,6,6-tetramethylpiperidine showed the formation of 2,2,6,6-tetramethylpiperidine-1-oxyl. Using [(18)O]-labeled triplet, ground state molecular oxygen [(18)O2 ((3)Σg(-))], chemical trapping of (18)O2 ((1)Δg) with disodium salt of anthracene-9,10-diyldiethane-2,1-diyl disulfate yielding the corresponding double-[(18)O]-labeled 9,10-endoperoxide, was detected through mass spectrometry. This corroborates formation of O2 ((1)Δg). Altogether, photoemission and chemical trapping studies clearly demonstrate that chemically and enzymatically nascent excited carbonyl generates (18)O2 ((1)Δg) by triplet-triplet energy transfer to ground state oxygen O2 ((3)Σg(-)), and supports the long formulated hypothesis of O2 ((1)Δg) involvement in physiological and pathophysiological events that might take place in tissues in the absence of light.

Singlet molecular oxygen generated by biological hydroperoxides

The chemistry behind the phenomenon of ultra-weak photon emission has been subject of considerable interest for decades. Great progress has been made on the understanding of the chemical generation of electronically excited states that are involved in these processes. Proposed mechanisms implicated the production of excited carbonyl species and singlet molecular oxygen in the mechanism of generation of chemiluminescence in biological system. In particular, attention has been focused on the potential generation of singlet molecular oxygen in the recombination reaction of peroxyl radicals by the Russell mechanism. In the last ten years, our group has demonstrated the generation of singlet molecular oxygen from reactions involving the decomposition of biologically relevant hydroperoxides, especially from lipid hydroperoxides in the presence of metal ions, peroxynitrite, HOCl and cytochrome c. In this review we will discuss details on the chemical aspects related to the mechanism of singlet molecular oxygen generation from different biological hydroperoxides.

Singlet molecular oxygen generation by light-activated DHN-melanin of the fungal pathogen Mycosphaerella fijiensis in black Sigatoka disease of bananas

In pathogenic fungi, melanin contributes to virulence, allowing tissue invasion and inactivation of the plant defence system, but has never been implicated as a factor for host cell death, or as a light-activated phytotoxin. Our research shows that melanin synthesized by the fungal banana pathogen Mycosphaerella fijiensis acts as a virulence factor through the photogeneration of singlet molecular oxygen O2 (1Δg). Using analytical tools, including elemental analysis, ultraviolet/infrared absorption spectrophometry and MALDI-TOF mass spectrometry analysis, we characterized both pigment content in mycelia and secreted to the culture media as 1,8-dihydroxynaphthalene (DHN)-melanin type compound. This is sole melanin-type in M. fijiensis. Isolated melanins irradiated with a Nd:YAG laser at 532 nm produced monomol light emission at 1270 nm, confirming generation of O2 (1Δg), a highly reactive oxygen specie (ROS) that causes cellular death by reacting with all cellular macromolecules. Intermediary polyketides accumulated in culture media by using tricyclazole and pyroquilon (two inhibitors of DHN-melanin synthesis) were identified by ESI-HPLC-MS/MS. Additionally, irradiation at 532 nm of that mixture of compounds and whole melanized mycelium also generated O2 (1Δg). A pigmented-strain generated more O2 (1Δg) than a strain with low melanin content. Banana leaves of cultivar Cavendish, naturally infected with different stages of black Sigatoka disease, were collected from field. Direct staining of the naturally infected leaf tissues showed the presence of melanin that was positively correlated to the disease stage. We also found hydrogen peroxide (H2O2) but we cannot distinguish the source. Our results suggest that O2 (1Δg) photogenerated by DHN-melanin may be involved in the destructive effects of Mycosphaerella fijiensis on banana leaf tissues. Further studies are needed to fully evaluate contributions of melanin-mediated ROS to microbial pathogenesis.

Elevated α-methyl-γ-hydroxy-1,N2-propano-2'-deoxyguanosine levels in urinary samples from individuals exposed to urban air pollution

Acetaldehyde and crotonaldehyde are genotoxic aldehydes present in tobacco smoke and vehicle exhaust. The reaction of these aldehydes with 2'-deoxyguanosine in DNA produces α-methyl-γ-hydroxy-1,N(2)-propano-2'-deoxyguanosine (1,N(2)-propanodGuo). Online HPLC-tandem mass spectrometry was utilized to accurately quantify 1,N(2)-propanodGuo in human urinary samples from 47 residents of São Paulo City (SP) and 35 residents of the rural municipality of São João da Boa Vista (SJBV) in the state of São Paulo. Significantly higher 1,N(2)-propanodGuo levels were found in the samples from SP donors than in samples from SJBV donors. Our results provide the first evidence that elevated levels of 1,N(2)-propanodGuo in urinary samples may be correlated with urban air pollution.

The development of a specific and sensitive LC-MS-based method for the detection and quantification of hydroperoxy- and hydroxydocosahexaenoic acids as a tool for lipidomic analysis

Docosahexaenoic acid (DHA) is an n-3 polyunsaturated fatty acid that is highly enriched in the brain, and the oxidation products of DHA are present or increased during neurodegenerative disease progression. The characterization of the oxidation products of DHA is critical to understanding the roles that these products play in the development of such diseases. In this study, we developed a sensitive and specific analytical tool for the detection and quantification of twelve major DHA hydroperoxide (HpDoHE) and hydroxide (HDoHE) isomers (isomers at positions 4, 5, 7, 8, 10, 11, 13, 14, 16, 17, 19 and 20) in biological systems. In this study, HpDoHE were synthesized by photooxidation, and the corresponding hydroxides were obtained by reduction with NaBH4. The isolated isomers were characterized by LC-MS/MS, and unique and specific fragment ions were chosen to construct a selected reaction monitoring (SRM) method for the targeted quantitative analysis of each HpDoHE and HDoHE isomer. The detection limits for the LC-MS/MS-SRM assay were 1-670 pg for HpDoHE and 0.5-8.5 pg for HDoHE injected onto a column. Using this method, it was possible to detect the basal levels of HDoHE isomers in both rat plasma and brain samples. Therefore, the developed LC-MS/MS-SRM can be used as an important tool to identify and quantify the hydro(pero)xy derivatives of DHA in biological system and may be helpful for the oxidative lipidomic studies.

DNA damage by singlet oxygen and cellular protective mechanisms

Reactive oxygen species, as singlet oxygen ((1)O(2)) and hydrogen peroxide, are continuously generated by aerobic organisms, and react actively with biomolecules. At excessive amounts, (1)O(2) induces oxidative stress and shows carcinogenic and toxic effects due to oxidation of lipids, proteins and nucleic acids. Singlet oxygen is able to react with DNA molecule and may induce G to T transversions due to 8-oxodG generation. The nucleotide excision repair, base excision repair and mismatch repair have been implicated in the correction of DNA lesions induced by (1)O(2) both in prokaryotic and in eukaryotic cells. (1)O(2) is also able to induce the expression of genes involved with the cellular responses to oxidative stress, such as NF-κB, c-fos and c-jun, and genes involved with tissue damage and inflammation, as ICAM-1, interleukins 1 and 6. The studies outlined in this review reinforce the idea that (1)O(2) is one of the more dangerous reactive oxygen species to the cells, and deserves our attention.

Long-term intermittent feeding, but not caloric restriction, leads to redox imbalance, insulin receptor nitration, and glucose intolerance

Calorie restriction is a dietary intervention known to improve redox state, glucose tolerance, and animal life span. Other interventions have been adopted as study models for caloric restriction, including nonsupplemented food restriction and intermittent, every-other-day feedings. We compared the short- and long-term effects of these interventions to ad libitum protocols and found that, although all restricted diets decrease body weight, intermittent feeding did not decrease intra-abdominal adiposity. Short-term calorie restriction and intermittent feeding presented similar results relative to glucose tolerance. Surprisingly, long-term intermittent feeding promoted glucose intolerance, without a loss in insulin receptor phosphorylation. Intermittent feeding substantially increased insulin receptor nitration in both intra-abdominal adipose tissue and muscle, a modification associated with receptor inactivation. All restricted diets enhanced nitric oxide synthase levels in the insulin-responsive adipose tissue and skeletal muscle. However, whereas calorie restriction improved tissue redox state, food restriction and intermittent feedings did not. In fact, long-term intermittent feeding resulted in largely enhanced tissue release of oxidants. Overall, our results show that restricted diets are significantly different in their effects on glucose tolerance and redox state when adopted long-term. Furthermore, we show that intermittent feeding can lead to oxidative insulin receptor inactivation and glucose intolerance.

Ultrasensitive simultaneous quantification of 1,N2-etheno-2'-deoxyguanosine and 1,N2-propano-2'-deoxyguanosine in DNA by an online liquid chromatography-electrospray tandem mass spectrometry assay

Exocyclic DNA adducts produced by exogenous and endogenous compounds are emerging as potential tools to study a variety of human diseases and air pollution exposure. A highly sensitive method involving online reverse-phase high performance liquid chromatography with electrospray tandem mass spectrometry detection in the multiple reaction monitoring mode and employing stable isotope-labeled internal standards was developed for the simultaneous quantification of 1,N(2)-etheno-2'-deoxyguanosine (1,N(2)-epsilondGuo) and 1,N(2)-propano-2'-deoxyguanosine (1,N(2)-propanodGuo) in DNA. This methodology permits direct online quantification of 2'-deoxyguanosine and ca. 500 amol of adducts in 100 microg of hydrolyzed DNA in the same analysis. Using the newly developed technique, accurate determinations of 1,N(2)-etheno-2'-deoxyguanosine and 1,N(2)-propano-2'-deoxyguanosine levels in DNA extracts of human cultured cells (4.01 +/- 0.32 1,N(2)-epsilondGuo/10(8) dGuo and 3.43 +/- 0.33 1,N(2)-propanodGuo/10(8) dGuo) and rat tissue (liver, 2.47 +/- 0.61 1,N(2)-epsilondGuo/10(8) dGuo and 4.61 +/- 0.69 1,N(2)-propanodGuo/10(8) dGuo; brain, 2.96 +/- 1.43 1,N(2)-epsilondGuo/10(8) dGuo and 5.66 +/- 3.70 1,N(2)-propanodGuo/10(8) dGuo; and lung, 0.87 +/- 0.34 1,N(2)-epsilondGuo/10(8) dGuo and 2.25 +/- 1.72 1,N(2)-propanodGuo/10(8) dGuo) were performed. The method described herein can be used to study the biological significance of exocyclic DNA adducts through the quantification of different adducts in humans and experimental animals with pathological conditions and after air pollution exposure.

Exocyclic DNA adducts as biomarkers of lipid oxidation and predictors of disease. Challenges in developing sensitive and specific methods for clinical studies

Exocyclic DNA adducts are emerging as potential new tools for the study of oxidative stress-related diseases as well as the determination of cancer etiology and cancer risk. It is important to determine whether levels of exocyclic DNA adducts reflect redox stress in vivo and what role these adducts play in human diseases. To answer these important questions, interindividual differences, tissue distribution, background levels, and repair have to be assessed. This review focuses on recent developments in the use of these adducts as possible biomarkers for disease risk related to oxidative stress and on the challenges in developing sensitive and specific methods for clinical studies.

Trypanosoma cruzi MSH2: Functional analyses on different parasite strains provide evidences for a role on the oxidative stress response

Components of the DNA mismatch repair (MMR) pathway are major players in processes known to generate genetic diversity, such as mutagenesis and DNA recombination. Trypanosoma cruzi, the protozoan parasite that causes Chagas disease has a highly heterogeneous population, composed of a pool of strains with distinct characteristics. Studies with a number of molecular markers identified up to six groups in the T. cruzi population, which showed distinct levels of genetic variability. To investigate the molecular basis for such differences, we analyzed the T. cruzi MSH2 gene, which encodes a key component of MMR, and showed the existence of distinct isoforms of this protein. Here we compared cell survival rates after exposure to genotoxic agents and levels of oxidative stress-induced DNA in different parasite strains. Analyses of msh2 mutants in both T. cruzi and T. brucei were also used to investigate the role of Tcmsh2 in the response to various DNA damaging agents. The results suggest that the distinct MSH2 isoforms have differences in their activity. More importantly, they also indicate that, in addition to its role in MMR, TcMSH2 acts in the parasite response to oxidative stress through a novel mitochondrial function that may be conserved in T. brucei.

Increased SOD1 association with chromatin, DNA damage, p53 activation, and apoptosis in a cellular model of SOD1-linked ALS

Mutations in the gene encoding cytosolic Cu,Zn-superoxide dismutase (SOD1) have been linked to familial amyotrophic lateral sclerosis (FALS). However the molecular mechanisms of motor neuron death are multi-factorial and remain unclear. Here we examined DNA damage, p53 activity and apoptosis in SH-SY5Y human neuroblastoma cells transfected to achieve low-level expression of either wild-type or mutant Gly(93)-->Ala (G93A) SOD1, typical of FALS. DNA damage was investigated by evaluating the levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) and DNA strand breaks. Significantly higher levels of DNA damage, increased p53 activity, and a greater percentage of apoptotic cells were observed in SH-SY5Y cells transfected with G93A SOD1 when compared to cells overexpressing wild-type SOD1 and untransfected cells. Western blot, FACS, and confocal microscopy analysis demonstrated that G93A SOD1 is present in the nucleus in association with DNA. Nuclear G93A SOD1 has identical superoxide dismutase activity but displays increased peroxidase activity when compared to wild-type SOD1. These results indicate that the G93A mutant SOD1 association with DNA might induce DNA damage and trigger the apoptotic response by activating p53. This toxic activity of mutant SOD1 in the nucleus may play an important role in the complex mechanisms associated with motor neuron death observed in ALS pathogenesis.

Thymine hydroperoxide as a potential source of singlet molecular oxygen in DNA

The decomposition of organic hydroperoxides into peroxyl radicals is a potential source of singlet molecular oxygen [O2 (1Deltag)] in biological systems. This study shows that 5-(hydroperoxymethyl)uracil (5-HPMU), a thymine hydroperoxide within DNA, reacts with metal ions or HOCl, generating O2 (1Deltag). Spectroscopic evidence for generation of O2 (1Deltag) was obtained by measuring (i) the bimolecular decay, (ii) the monomolecular decay, and (iii) the observation of D2O enhancement of O2 (1Deltag) production and the quenching effect of NaN3. Moreover, the presence of O2 (1Deltag) was unequivocally demonstrated by the direct characterization of the near-infrared light emission. For the sake of comparison, O2 (1Deltag) derived from the H2O2/HOCl system and from the thermolysis of the N,N'-di(2,3-dihydroxypropyl)-1,4-naphthalenedipropanamide endoperoxide was also monitored. More evidence of O2 (1Deltag) generation was obtained by chemical trapping of O2 (1Deltag) with anthracene-9,10-divinylsulfonate (AVS) and detection of the specific AVS endoperoxide by HPLC/MS/MS. The detection by HPLC/MS of 5-(hydroxymethyl)uracil and 5-formyluracil, two thymine oxidation products generated from the reaction of 5-HPMU and Ce4+ ions, supports the Russell mechanism. These photoemission properties and chemical trapping clearly demonstrate that the decomposition of 5-HPMU generates O2 (1Deltag) by the Russell mechanism and point to the involvement of O2 (1Deltag) in thymidine hydroperoxide cytotoxicity.

Mild mitochondrial uncoupling in mice affects energy metabolism, redox balance and longevity

Caloric restriction is the most effective non-genetic intervention to enhance lifespan known to date. A major research interest has been the development of therapeutic strategies capable of promoting the beneficial results of this dietary regimen. In this sense, we propose that compounds that decrease the efficiency of energy conversion, such as mitochondrial uncouplers, can be caloric restriction mimetics. Treatment of mice with low doses of the protonophore 2,4-dinitrophenol promotes enhanced tissue respiratory rates, improved serological glucose, triglyceride and insulin levels, decrease of reactive oxygen species levels and tissue DNA and protein oxidation, as well as reduced body weight. Importantly, 2,4-dinitrophenol-treated animals also presented enhanced longevity. Our results demonstrate that mild mitochondrial uncoupling is a highly effective in vivo antioxidant strategy, and describe the first therapeutic intervention capable of effectively reproducing the physiological, metabolic and lifespan effects of caloric restriction in healthy mammals.

Biological hydroperoxides and singlet molecular oxygen generation

The decomposition of lipid hydroperoxides (LOOH) into peroxyl radicals is a potential source of singlet molecular oxygen ((1)O(2)) in biological systems. Recently, we have clearly demonstrated the generation of (1)O(2) in the reaction of lipid hydroperoxides with biologically important oxidants such as metal ions, peroxynitrite and hypochlorous acid. The approach used to unequivocally demonstrate the generation of (1)O(2) in these reactions was the use of an isotopic labeled hydroperoxide, the (18)O-labeled linoleic acid hydroperoxide, the detection of labeled compounds by HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) and the direct spectroscopic detection and characterization of (1)O(2) light emission. Using this approach we have observed the formation of (18)O-labeled (1)O(2) by chemical trapping of (1)O(2) with anthracene derivatives and detection of the corresponding labeled endoperoxide by HPLC-MS/MS. The generation of (1)O(2) was also demonstrated by direct spectral characterization of (1)O(2) monomol light emission in the near-infrared region (lambda = 1270 nm). In summary, our studies demonstrated that LOOH can originate (1)O(2). The experimental evidences indicate that (1)O(2) is generated at a yield close to 10% by the Russell mechanism, where a linear tetraoxide intermediate is formed in the combination of two peroxyl radicals. In addition to LOOH, other biological hydroperoxides, including hydroperoxides formed in proteins and nucleic acids, may also participate in reactions leading to the generation (1)O(2). This hypothesis is currently being investigated in our laboratory.

Covalent modification of cytochrome c exposed to trans,trans-2,4-decadienal

Modification of biomolecules by reactive aldehydes is believed to play a role in biological processes, including aging, atherosclerosis, and Alzheimer's disease. Here, the modification of cytochrome c promoted by trans, trans-2,4-decadienal (DDE) was investigated. Matrix-assisted laser desorption/ionization time-of-flight experiments indicated increases in the molecular weight of cytochrome c, consistent with the formation of DDE adducts. Our data show that the protein modification was time-, pH-, and DDE concentration-dependent, leading to the formation of at least six adducts after 2 h of incubation at pH 7.4. Electrospray ionization quantitative TOF mass spectrometry analysis of tryptic digests indicated that His-33, Lys-39, Lys-72, and Lys-100 were modified by DDE. These adducts could have significant effects considering that His-33, Lys-72, and Lys-100 are present in clusters of basic amino acid residues, which are believed to participate in the interaction of cytochrome c with cardiolipin in the inner mitochondrial membrane and cytochrome c oxidase. A blue shift in the cytochrome c Soret band from 409 to 406 nm was also observed after DDE reaction, indicating heme crevice opening and displacement of heme sixth ligand (Met-80) coordination in modified protein. The covalent modifications in cytochrome c could play a role in mitochondrial dysfunction associated with oxidative stress.

Flow Injection Amperometric Detection of 2‘-Deoxyguanosine at a Ruthenium Oxide Hexacyanoferrate Modified Electrode

A ruthenium oxide hexacyanoferrate (RuOHCF) modified electrode was developed. Hydrodynamic voltammetry was employed to demonstrate the remarkable electrocatalytic activity toward the oxidation of 2'-deoxyguanosine. The RuOHCF modified electrode was used as amperometric detector for 2'-deoxyguanosine determination in a FIA apparatus. The influence of various experimental conditions was explored for optimum analytical performance, and at these experimental conditions, the method exhibited a linear response range to 2'-deoxyguanosine extending from 3.8 to 252 micromol L(-1) with detection limit of 94 nmol L(-1). Applications in DNA samples were examined, and the results for determination of 2'-deoxyguanosine were in good agreement with those obtained by HPLC analysis. Studies on the kinetics of the in vitro consumption of 2'-deoxyguanosine by acetaldehyde were also performed.