Lipid hydroperoxides as a source of singlet molecular oxygen

Significance of Singlet Oxygen Molecule in Pathologies

Reactive oxygen species, including singlet oxygen, play an important role in the onset and progression of disease, as well as in aging. Singlet oxygen can be formed non-enzymatically by chemical, photochemical, and electron transfer reactions, or as a byproduct of endogenous enzymatic reactions in phagocytosis during inflammation. The imbalance of antioxidant enzymes and antioxidant networks with the generation of singlet oxygen increases oxidative stress, resulting in the undesirable oxidation and modification of biomolecules, such as proteins, DNA, and lipids. This review describes the molecular mechanisms of singlet oxygen production in vivo and methods for the evaluation of damage induced by singlet oxygen. The involvement of singlet oxygen in the pathogenesis of skin and eye diseases is also discussed from the biomolecular perspective. We also present our findings on lipid oxidation products derived from singlet oxygen-mediated oxidation in glaucoma, early diabetes patients, and a mouse model of bronchial asthma. Even in these diseases, oxidation products due to singlet oxygen have not been measured clinically. This review discusses their potential as biomarkers for diagnosis. Recent developments in singlet oxygen scavengers such as carotenoids, which can be utilized to prevent the onset and progression of disease, are also described.

Effects of histamine and sodium hypochlorite on prooxidand state in the rats erytrocytes

We studied the simultaneous influence of histamine and sodium hypochlorite (SH) on lipid peroxidation processes, as well as the level of structural changes in membranes (via the content of sialic acid) in rat erythrocytes. We established that histamine affects lipid peroxidation processes with the formation of lipid hydroperoxides, damages proteins and reduces the content of sialic acids, which leads to changes in the surface charge of red blood cells. However, the simultaneous action of histamine and low SH concentration has a positive effect in that it corrects the pro-oxidant state of erythrocytes. Hence, the content of lipid hydroperoxides, TBA-active products, carbonyl groups of proteins and sialic acids were mainly reduced after the simultaneous action of histamine and SH at all studied concentrations during the rehabilitation period.

Reactive Oxygen Species as a Response to Wounding: In Vivo Imaging in Arabidopsis thaliana

Mechanical injury or wounding in plants can be attributed to abiotic or/and biotic causes. Subsequent defense responses are either local, i.e. within or in the close vicinity of affected tissue, or systemic, i.e. at distant plant organs. Stress stimuli activate a plethora of early and late reactions, from electric signals induced within seconds upon injury, oxidative burst within minutes, and slightly slower changes in hormone levels or expression of defense-related genes, to later cell wall reinforcement by polysaccharides deposition, or accumulation of proteinase inhibitors and hydrolytic enzymes. In the current study, we focused on the production of reactive oxygen species (ROS) in wounded Arabidopsis leaves. Based on fluorescence imaging, we provide experimental evidence that ROS [superoxide anion radical (O₂ ^•-) and singlet oxygen (¹O₂)] are produced following wounding. As a consequence, oxidation of biomolecules is induced, predominantly of polyunsaturated fatty acid, which leads to the formation of reactive intermediate products and electronically excited species.

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.

Prevention of memory impairment induced by post-traumatic stress disorder by cerebrolysin

Post-traumatic stress disorder (PTSD) may occur after exposure to stressful, fearful or troubling events. Until now, there is no curable medication for this disorder. Cerebrolysin is a neuropeptide, which has an important role in the treatment of vascular dementia. In this study, the probable protective effect of cerebrolysin on PTSD-induced memory impairment was investigated. To induce PTSD, the single prolonged stress (SPS) model was used. Rats were allocated into four groups: control (vehicle-treated), CBL (administrated cerebrolysin 2.5 ml/kg by intraperitoneal route for 4 weeks), SPS (as a model of PTSD and administered vehicle), and CBL-SPS (exposed to SPS and administered cerebrolysin for 4 weeks). Learning and memory were assessed using the radial arm water maze (RAWM). Results showed that SPS impaired both short- and long- term memories; and chronic cerebrolysin administration prevented such effect. Cerebrolysin also prevented decreases in hippocampal GSH levels and GSH/GSSG ratios, and increased GSSG and TBARs, levels induced by PTSD. In conclusion, a protective effect of cerebrolysin administration against SPS model of PTSD induced short- and long- term memory impairment was characterized. This protection could be accomplished, at least partly, by prevention of PTSD induced increase in oxidative stress in the hippocampus via the use of cerebrolysin.

Effect on oxidative stress, hepatic chemical metabolizing parameters, and genotoxic damage of mad honey intake in rats

A total of 66 male Wistar rats were used and six groups (control: 10 animals and experimental: 12 animals) were formed. While a separate control group was established for each study period, mad honey application to the animals in the experimental group was carried out with a single dose (12.5 g kg−1 body weight (b.w.); acute stage), at a dose of 7.5 g kg−1 b.w. for 21 days (subacute stage), and at a dose of 5 g kg−1 b.w. for 60 days (chronic stage). Tissue and blood oxidative stress markers (malondialdehyde (MDA), nitric oxide (NO), 4-hydroxynonenal (HNE), superoxide dismutase, catalase, glutathione (GSH) peroxidase, and glucose-6-phosphate dehydrogenase), hepatic chemical metabolizing parameters in the liver (cytochrome P450 2E1, nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase, nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome c reductase (CYTC), GSH S-transferase (GST), and GSH), and micronucleus and comet test in some samples were examined. Findings from the study showed that single and repeated doses given over the period increased MDA, NO, and HNE levels while decreasing/increasing tissue and blood antioxidant enzyme activities. From hepatic chemical metabolizing parameters, GST activity increased in the subacute and chronic stages and CYTC activity increased in the acute period, whereas GSH level decreased in the subacute stage. Changes in tail and head intensities were found in most of the comet results. Mad honey caused oxidative stresses for each exposure period and made some significant changes on the comet test in certain periods for some samples obtained. In other words, according to the available research results obtained, careless consumption of mad honey for different medical purposes is not appropriate.

Phagocyte NADPH oxidase, oxidative stress and lipids: Anti- or pro ageing?

The role of NADPH oxidase in ageing is debated because of the dual roles of free radicals, toxic though necessary. In this paper we summarize some results about two aspects linked to the regulation of the activity of phagocyte NADPH oxidase (Nox2), encountered frequently in elderly people: inflammation and hypercholesterolemia. In the presence of a high amount of reactive oxygen species (ROS) created by itself or by any other source, the enzyme activity is mostly lowered. Oxidation of the membrane and/or of one of the cytosolic partners could be responsible for this loss of activity. However using a cell free system, we had also shown that a low amount of ROS could activate this enzyme. Similarly, cholesterol has a similar dual role, either activating or inhibiting. In in vitro cell free system with neutrophil membranes from healthy donors, the addition, as well as the removal of cholesterol, diminishes the Nox2 activity. The activity of Nox2 is lowered in neutrophils of untreated hypercholesterolemic patients. Finally oxysterols (25-hydroxy-cholesterol or 5α, 6α - epoxy-cholesterol) do not induce effects different from that of non-oxidized cholesterol. These findings are in agreement with the Janus role of NADPH oxidase, the main source of non-mitochondrial ROS.

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.

Paraoxonase and arylesterase levels in autoimmune thyroid diseases

OBJECTIVE

The aim of this study was to evaluate serum paraoxonase-1 (PON1) activity and its association with oxidative stress in autoimmune thyroid disease (AITD).

METHODS

A total of 50 patients with AITD, including 25 with Hashimoto's thyroiditis and 25 with Graves' disease were enrolled. The control group comprised 27 healthy subjects. Blood samples were obtained in the euthyroid period and 3 months after initiation of medical treatment. Serum samples from patients with AITD and the healthy control group were analyzed for basal PON1, salt-stimulated PON1, and arylesterase (ARE) activities, along with lipid hydroperoxide (LOOH) and total free sulfhydryl (-SH) levels.

RESULTS

Serum PON1 activities and -SH levels were significantly lower (P < 0.001, for each), whereas LOOH levels were significantly higher (P < 0.001, for each) in patients with AITD, compared to the control group. We observed no significant differences in ARE levels between the patient and healthy control groups (P > 0.05). PON1 activity was positively correlated with -SH (r = 0.522, P < 0.001) and negatively correlated with LOOH (r = -0.487, P < 0.001). PON1 phenotype distribution of the subjects was not significantly different among the three groups (P = 0.961).

CONCLUSIONS

Serum PON1 activity is decreased in patients with AITD, and correlated positively with -SH, a well-known antioxidant, and negatively with LOOH, an index of lipid oxidation.

Preparation for oxidative stress under hypoxia and metabolic depression: Revisiting the proposal two decades later

Organisms that tolerate wide variations in oxygen availability, especially to hypoxia, usually face harsh environmental conditions during their lives. Such conditions include, for example, lack of food and/or water, low or high temperatures, and reduced oxygen availability. In contrast to an expected strong suppression of protein synthesis, a great number of these animals present increased levels of antioxidant defenses during oxygen deprivation. These observations have puzzled researchers for more than 20 years. Initially, two predominant ideas seemed to be irreconcilable: on one hand, hypoxia would decrease reactive oxygen species (ROS) production, while on the other the induction of antioxidant enzymes would require the overproduction of ROS. This induction of antioxidant enzymes during hypoxia was viewed as a way to prepare animals for oxidative damage that may happen ultimately during reoxygenation. The term "preparation for oxidative stress" (POS) was coined in 1998 based on such premise. However, there are many cases of increased oxidative damage in several hypoxia-tolerant organisms under hypoxia. In addition, over the years, the idea of an assured decrease in ROS formation under hypoxia was challenged. Instead, several findings indicate that the production of ROS actually increases in response to hypoxia. Recently, it became possible to provide a comprehensive explanation for the induction of antioxidant enzymes under hypoxia. The supporting evidence and the limitations of the POS idea are extensively explored in this review as we discuss results from research on estivation and situations of low oxygen stress, such as hypoxia, freezing exposure, severe dehydration, and air exposure of water-breathing animals. We propose that, under some level of oxygen deprivation, ROS are overproduced and induce changes leading to hypoxic biochemical responses. These responses would occur mainly through the activation of specific transcription factors (FoxO, Nrf2, HIF-1, NF-κB, and p53) and post translational mechanisms, both mechanisms leading to enhanced antioxidant defenses. Moreover, reactive nitrogen species are candidate modulators of ROS generation in this scenario. We conclude by drawing out the future perspectives in this field of research, and how advances in the knowledge of the mechanisms involved in the POS strategy will offer new and innovative study scenarios of biological and physiological cellular responses to environmental stress.

Understanding DNA under oxidative stress and sensitization: the role of molecular modeling

DNA is constantly exposed to damaging threats coming from oxidative stress, i.e., from the presence of free radicals and reactive oxygen species. Sensitization from exogenous and endogenous compounds that strongly enhance the frequency of light-induced lesions also plays an important role. The experimental determination of DNA lesions, though a difficult subject, is somehow well established and allows to elucidate even extremely rare DNA lesions. In parallel, molecular modeling has become fundamental to clearly understand the fine mechanisms related to DNA defects induction. Indeed, it offers an unprecedented possibility to get access to an atomistic or even electronic resolution. Ab initio molecular dynamics may also describe the time-evolution of the molecular system and its reactivity. Yet the modeling of DNA (photo-)reactions does necessitate elaborate multi-scale methodologies to tackle a damage induction reactivity that takes place in a complex environment. The double-stranded DNA environment is first characterized by a very high flexibility, but also a strongly inhomogeneous electrostatic embedding. Additionally, one aims at capturing more subtle effects, such as the sequence selectivity which is of critical important for DNA damage. The structure and dynamics of the DNA/sensitizers complexes, as well as the photo-induced electron- and energy-transfer phenomena taking place upon sensitization, should be carefully modeled. Finally the factors inducing different repair ratios for different lesions should also be rationalized. In this review we will critically analyze the different computational strategies used to model DNA lesions. A clear picture of the complex interplay between reactivity and structural factors will be sketched. The use of proper multi-scale modeling leads to the in-depth comprehension of DNA lesions mechanisms and also to the rational design of new chemo-therapeutic agents.