Generation of electronically excited triplet species at the cellular level: a potential source of genotoxicity

Myocardial infarction and oxidative damage in animal models: objective and expectations from the application of cysteine derivatives

Reactive oxygen species (ROS) and associated oxidative stress are the main contributors to pathophysiological changes following myocardial infarction (MI), which is the principal cause of death from cardiovascular disease. The glutathione (GSH)/glutathione peroxidase (GPx) system appears to be the main and most active cardiac antioxidant mechanism. Hence, enhancement of the myocardial GSH system might have protective effects in the setting of MI. It follows that by increasing antioxidant capacity, the heart will be able to reduce the damage associated with MI and even prevent/weaken the occurrence of oxidative stress, which is highly ranked among the factors responsible for the occurrence of acute MI. For these reasons, the primary goal of future investigations should be to address the effects of different antioxidative compounds and especially cysteine derivatives like N-acetyl cysteine (NAC) and L-2-oxothiazolidine-4-carboxylic acid (OTC) as precursors responsible for the enhancement of the GSH-related antioxidant system's capacity. It is assumed that this will lay down the basis for elucidation of the mechanisms throughout which applicable doses of OTC will manifest a potentially positive impact in the reduction of adverse effects of acute MI. The inclusion of OTC in the models for prediction of the distribution of oxygen in infarcted animal hearts can help to upgrade existing computational models. Such a model would be based on computational geometries of the heart, but the inclusion of biochemical redox features in addition to angiogenic therapy, despite improvement of the post-infarcted oxygenated outcome could enhance the accuracy of the predictive values of oxygenation.

Unexpected Reaction Pathway of the Alpha-Aminoalkyl Radical Derived from One-Electron Oxidation of S-Alkylglutathiones

Laser flash photolysis and high-resolution mass spectrometry were used to investigate the mechanism of one-electron oxidation of two S-alkylglutathiones using 3-carboxybenzophenone (3CB) as a photosensitizer. This report indicates an unexpected reaction pathway of the α-aminoalkyl radical cation (αN⁺) derived from the oxidation of S-alkylglutathiones. Instead of a common hydrolysis reaction of αN⁺ reported earlier for methionine and other sulfur-containing aminoacids and peptides, an intramolecular ring-closure reaction was found for S-alkylglutathiones.

Mechanism of the Formation of Electronically Excited Species by Oxidative Metabolic Processes: Role of Reactive Oxygen Species

It is well known that biological systems, such as microorganisms, plants, and animals, including human beings, form spontaneous electronically excited species through oxidative metabolic processes. Though the mechanism responsible for the formation of electronically excited species is still not clearly understood, several lines of evidence suggest that reactive oxygen species (ROS) are involved in the formation of electronically excited species. This review attempts to describe the role of ROS in the formation of electronically excited species during oxidative metabolic processes. Briefly, the oxidation of biomolecules, such as lipids, proteins, and nucleic acids by ROS initiates a cascade of reactions that leads to the formation of triplet excited carbonyls formed by the decomposition of cyclic (1,2-dioxetane) and linear (tetroxide) high-energy intermediates. When chromophores are in proximity to triplet excited carbonyls, the triplet-singlet and triplet-triplet energy transfers from triplet excited carbonyls to chromophores result in the formation of singlet and triplet excited chromophores, respectively. Alternatively, when molecular oxygen is present, the triplet-singlet energy transfer from triplet excited carbonyls to molecular oxygen initiates the formation of singlet oxygen. Understanding the mechanism of the formation of electronically excited species allows us to use electronically excited species as a marker for oxidative metabolic processes in cells.

Transketolase Is Identified as a Target of Herbicidal Substance α-Terthienyl by Proteomics

α-terthienyl is a natural phytotoxin isolated originally from Flaveria bidentis (L.) Kuntze. The bioassay presented here shows the strong herbicidal activity of α-terthienyl on Digitaria sanguinalis, Arabidopsis thaliana and Chlamydomonas reinhardtii. The α-terthienyl-induced response of A. thaliana at the protein level was analyzed at different times. Changes in the protein expression profiles were analyzed by two-dimensional gel electrophoresis and liquid chromatography tandem mass spectrometry (LC-MS/MS) mass spectrometry. Sixteen protein spots were identified that showed reproducible changes in the expression of at least 2-fold when compared to the control. Among these 16 spots, three were up-regulated and 13 were down-regulated. The decreased expression of several proteins associated with energy production and carbon metabolism suggested that these processes were affected by α-terthienyl. To search for the candidate proteins in this screen, A. thaliana T-DNA mutants of the candidate proteins were used to test their susceptibility to α-terthienyl. Amongst the others, attkl1, a mutant of transketolase, exhibited a significantly lower sensitivity to α-terthienyl when hit compared with Col-0. Based on the identification of the proteins associated with the response to α-terthienyl by proteomics, a candidate target protein transketolase was identified.

Lipoxygenase in singlet oxygen generation as a response to wounding: in vivo imaging in Arabidopsis thaliana

Wounding, one of the most intensive stresses influencing plants ontogeny and lifespan, can be induced by herbivory as well as by physical factors. Reactive oxygen species play indispensable role both in the local and systemic defense reactions which enable "reprogramming" of metabolic pathways to set new boundaries and physiological equilibrium suitable for survival. In our current study, we provide experimental evidence on the formation of singlet oxygen (¹O₂) after wounding of Arabidopsis leaves. It is shown that ¹O₂ is formed by triplet-triplet energy transfer from triplet carbonyls to molecular oxygen. Using lipoxygenase inhibitor catechol, it is demonstrated that lipid peroxidation is initiated by lipoxygenase. Suppression of ¹O₂ formation in lox2 mutant which lacks chloroplast lipoxygenase indicates that lipoxygenase localized in chloroplast is predominantly responsible for ¹O₂ formation. Interestingly, ¹O₂ formation is solely restricted to chloroplasts localized at the wounding site. Data presented in this study might provide novel insight into wound-induced signaling in the local defense reaction.

Singlet oxygen production in Chlamydomonas reinhardtii under heat stress

In the current study, singlet oxygen formation by lipid peroxidation induced by heat stress (40 °C) was studied in vivo in unicellular green alga Chlamydomonas reinhardtii. Primary and secondary oxidation products of lipid peroxidation, hydroperoxide and malondialdehyde, were generated under heat stress as detected using swallow-tailed perylene derivative fluorescence monitored by confocal laser scanning microscopy and high performance liquid chromatography, respectively. Lipid peroxidation was initiated by enzymatic reaction as inhibition of lipoxygenase by catechol and caffeic acid prevented hydroperoxide formation. Ultra-weak photon emission showed formation of electronically excited species such as triplet excited carbonyl, which, upon transfer of excitation energy, leads to the formation of either singlet excited chlorophyll or singlet oxygen. Alternatively, singlet oxygen is formed by direct decomposition of hydroperoxide via Russell mechanisms. Formation of singlet oxygen was evidenced by the nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl detected by electron paramagnetic resonance spin-trapping spectroscopy and the imaging of green fluorescence of singlet oxygen sensor green detected by confocal laser scanning microscopy. Suppression of singlet oxygen formation by lipoxygenase inhibitors indicates that singlet oxygen may be formed via enzymatic lipid peroxidation initiated by lipoxygenase.

The formation of electronically excited species in the human multiple myeloma cell suspension

In this study, evidence is provided on the formation of electronically excited species in human multiple myeloma cells U266 in the growth medium exposed to hydrogen peroxide (H2O2). Two-dimensional imaging of ultra-weak photon emission using highly sensitive charge coupled device camera revealed that the addition of H2O2 to cell suspension caused the formation of triplet excited carbonyls (3)(R = O)*. The kinetics of (3)(R = O)* formation in the real time, as measured by one-dimensional ultra-weak photon emission using low-noise photomultiplier, showed immediate enhancement followed by a slow decay. In parallel to the formation of (3)(R = O)*, the formation of singlet oxygen ((1)O2) in U266 cells caused by the addition of H2O2 was visualized by the imaging of (1)O2 using the green fluorescence of singlet oxygen sensor green detected by confocal laser scanning microscopy. Additionally, the formation of (1)O2 after the addition of H2O2 to cell suspension was detected by electron paramagnetic resonance spin-trapping spectroscopy using 2,2,6,6-tetramethyl-4-piperidone. Presented results indicate that the addition of H2O2 to cell suspension results in the formation of (3)(R = O)* and (1)O2 in U266 cell suspension. The contribution of the cell-free medium to the formation of electronically excited species was discussed.

Role of reactive oxygen species in ultra-weak photon emission in biological systems

Ultra-weak photon emission originates from the relaxation of electronically excited species formed in the biological systems such as microorganisms, plants and animals including humans. Electronically excited species are formed during the oxidative metabolic processes and the oxidative stress reactions that are associated with the production of reactive oxygen species (ROS). The review attempts to overview experimental evidence on the involvement of superoxide anion radical, hydrogen peroxide, hydroxyl radical and singlet oxygen in both the spontaneous and the stress-induced ultra-weak photon emission. The oxidation of biomolecules comprising either the hydrogen abstraction by superoxide anion and hydroxyl radicals or the cycloaddition of singlet oxygen initiate a cascade of oxidative reactions that lead to the formation of electronically excited species such as triplet excited carbonyl, excited pigments and singlet oxygen. The photon emission of these electronically excited species is in the following regions of the spectrum (1) triplet excited carbonyl in the near UVA and blue-green areas (350-550nm), (2) singlet and triplet excited pigments in the green-red (550-750nm) and red-near IR (750-1000nm) areas, respectively and (3) singlet oxygen in the red (634 and 703nm) and near IR (1270nm) areas. The understanding of the role of ROS in photon emission allows us to use the spontaneous and stress-induced ultra-weak photon emission as a non-invasive tool for monitoring of the oxidative metabolic processes and the oxidative stress reactions in biological systems in vivo, respectively.

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.

The oxidation of cyclic sulfides by tetramethyldioxetane and the isobutanal/O2/peroxidase system: oxygen transfer versus electron transfer

The oxidation of chlorpromazine (CPZ) by tetramethyldioxetane (TMD) and isobutanal (IBAL)/O2/horseradish peroxidase (HRP) system was investigated. The reaction with TMD proved to be of the oxygen transfer type, generating chlorpromazine-5-oxide (CPZO) and tetramethylethylene-oxide, and not by single-electron transfer, as previously reported. In contrast, the reaction of CPZ with IBAL/O2/HRP leads to formation of chlorpromazine cation radical, through reaction with active intermediates Compound I and II, following its dismutation and hydrolysis to CPZO. For comparison, 10-methylphenothiazine was also tested. Despite the fact that both systems are known to generate oxidizing triplet acetone, this species does not participate in the oxidation path in either case.