The role of EPR spectroscopy in studies of the oxidative status of biological systems and the antioxidative properties of various compounds

New potential biomarker for stratification of patients for pharmacological vitamin C in adjuvant settings of cancer therapy

Our graphical review expands the analysis of cancer vulnerabilities for high dose vitamin C, based on several facts, illustrating the cytotoxic potential of the ascorbate free radical (AFR) via impairment of mitochondrial respiration and the mechanisms of its elimination in mammals by the membrane-bound NADH:cytochrome b5 oxidoreductase 3 (Cyb5R3). We propose that vitamin C can function in “protective mode” or “destructive mode” affecting cellular homeostasis, depending on the intracellular “steady-state” concentration of AFR and differential expression/activity of Cyb5R3 in cancerous and normal cells. Thus, a specific anti-cancer effect can be achieved at high doses of vitamin C therapy. The review is intended for a wide audience of readers – from students to specialists in the field.

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The ascorbate radical could impair mitochondrial respiration via cytochrome c reduction.

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The ascorbate radical could mediate the imbalance of the coenzyme Q “pool” in cancer cells.

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The selective cytotoxicity of vitamin C in cancer could be mediated by Cyb5R3/VDAC1.

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Low/normal doses of vitamin C act in a “protective mode” for normal/cancer cells.

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High doses of vitamin C act in a “destructive mode” for cancer cells only.

Antioxidant and prooxidant effects of Piptadeniastrum africanum as the possible rationale behind its broad scale application in African ethnomedicine

ETHNOPHARMACOLOGICAL RELEVANCE

Piptadeniastrum africanum is widely used in treating oxidative stress related diseases. Oxidative stress, defined as the disturbance in the balance between the production of free radicals and antioxidant defenses, is the root cause of many pathophysiological conditions. Based on the dual properties of prooxidants as toxic and beneficial compounds, both prooxidants and antioxidants may be effective in the treatment of these conditions when the right dose is given to the right subject at the right time for the right duration.

AIM OF THE STUDY

This study was aimed at investigating the in vitro and ex vivo anti- and pro-oxidative effects of P. africanum.

MATERIALS AND METHODS

Total phenolic and flavonoid contents of methanol and aqueous extracts of P. africanum stem back were quantified spectrophotometrically. The methanol extract, ascorbate radicals and reactive oxygen species in brain and liver homogenates of mice treated with the methanol stem bark extract were analyzed by electron paramagnetic resonance (EPR) spectroscopy. Free radical scavenging of DPPH was determined by spectrophotometric and EPR assays.

RESULTS

The methanol extract was richer in both phenolic and flavonoid contents compared to the aqueous extracts and also showed better DPPH radical scavenging capacity. The EPR spectroscopy in vitro analysis exhibited high DPPH scavenging capacity before and after UV irradiation (99.5% and 98.76%) at 40 μg/ml extract. The ex vivo EPR spectroscopy studies demonstrated increased levels of ascorbate radicals (•Asc) in liver and brain homogenates of healthy mice treated with P. africanum in comparison with those of the non treated controls (0.6141 ± 0.026 vs 0.1800 ± 0.0073 arb. units for liver homogenates and 0.9605 ± 0.0492 vs 0.3375 ± 0.0062 arb. units for brain homogenates, correspondingly). Considerably, higher levels of reactive oxygen species (ROS) were measured in mice liver and brain homogenates after treatment with P. africanum extract compared to the control group, as well (1.9402 ± 0.1200 vs 0.6699 ± 0.062 arb. units for liver homogenates and 1.7325 ± 01503 vs 0.3167 ± 0.0403 arb.units, respectively).

CONCLUSION

Therefore, P. africanum exhibited antioxidant and pro-oxidant properties which may explain its broad spectrum use in a wide variety of ailments.

Structural and biochemical response of chloroplasts in tolerant and sensitive barley genotypes to drought stress

The aim of this research was to characterize the changes of structural organization of chloroplasts of sensitive (Maresi) and tolerant (Cam/B1) barley genotypes upon soil drought (10days), which was applied in two stages of plant growth, i.e. seedlings and flag leaves. The electron paramagnetic resonance (EPR) technique was used for the determination of changes in the concentration and nature of long-lived radicals and metal ions (Mn, Fe), measured directly in the structures of fresh leaves, occurring after stress treatment. Stronger variations of EPR parameters were found after drought stress application in the flag-leaf phase and for sensitive genotype. Chloroplasts of Cam/B1 were characterized by a larger surface area and less degradation of their structure during drought stress in comparison to Maresi. The data obtained from Raman spectra showed that better stress tolerance of the genotype was accompanied by greater accumulation of carotenoids in chloroplasts and was correlated with an increase in carotenoid radicals. The increase of the value of the electrokinetic potential (relative to control), which was slightly larger for the chloroplasts of Maresi than of Cam/B1, indicated the chemical reconstruction of the membrane leading to a reduction of their polarity during drought action.

Protective effect of two essential oils isolated from Rosa damascena Mill. and Lavandula angustifolia Mill, and two classic antioxidants against L-dopa oxidative toxicity induced in healthy mice

Levodopa (L-dopa) is a "gold standard" and most effective symptomatic agent in the Parkinson's disease (PD) treatment. The several treatments have been developed in an attempt to improve PD treatment, but most patients were still levodopa dependent. The issue of toxicity was raised in vitro studies, and suggests that L-dopa can be toxic to dopaminergic neurons, but it is not yet entirely proven. L-dopa prolonged treatment is associated with motor complications and some limitations. Combining the L-dopa therapy with antioxidants can reduce related sideeffects and provide symptomatic relief. The natural antioxidants can be isolated from any plant parts such as seeds, leaves, roots, bark, etc., and their extracts riched in phenols can retard the oxidative degradation of the lipids, proteins and DNA. Thus, study suggests that combination of essential oils (Rose oil and Lavender oil), Vitamin C and Trolox with Ldopa can reduce oxidative toxicity, and may play a key role in ROS/RNS disarm.

Superoxide Ion: Generation and Chemical Implications

Superoxide ion (O2(•-)) is of great significance as a radical species implicated in diverse chemical and biological systems. However, the chemistry knowledge of O2(•-) is rather scarce. In addition, numerous studies on O2(•-) were conducted within the latter half of the 20th century. Therefore, the current advancement in technology and instrumentation will certainly provide better insights into mechanisms and products of O2(•-) reactions and thus will result in new findings. This review emphasizes the state-of-the-art research on O2(•-) so as to enable researchers to venture into future research. It comprises the main characteristics of O2(•-) followed by generation methods. The reaction types of O2(•-) are reviewed, and its potential applications including the destruction of hazardous chemicals, synthesis of organic compounds, and many other applications are highlighted. The O2(•-) environmental chemistry is also discussed. The detection methods of O2(•-) are categorized and elaborated. Special attention is given to the feasibility of using ionic liquids as media for O2(•-), addressing the latest progress of generation and applications. The effect of electrodes on the O2(•-) electrochemical generation is reviewed. Finally, some remarks and future perspectives are concluded.

Changes of paramagnetic species in cereal grains upon short-term ozone action as a marker of oxidative stress tolerance

The increase of the concentration of ozone in the atmosphere, being the direct source of reactive oxygen species, results in the yield loss of agronomic crops. On the other hand, ozone is also used as a protector against microorganisms, living in plants and present in materials obtained from them, dangerous for human and animal health. In this work it has been studied if ozone in doses similar to those used for removal of microorganisms can have significant influence on the generation of stable organic radicals and changes in the character of transition metal ions and in the antioxidative biochemical parameters of cereal grains. The aim of this work was to find if the response of grains of three cereals (wheat, oat and barley) to ozone depended on their oxidative stress tolerance. The influence of direct short-term ozone application on grains of these cereals, each represented by two genotypes with different oxidative stress tolerance, was studied by biochemical analyses and by electron paramagnetic resonance (EPR) technique. Whole grains as well as their parts: embryo, endosperm and seed coat were subjected to ozone treatment for 30 min. Biochemical investigation of control samples showed that their antioxidant activity increased in order: wheat<oat<barley. EPR method revealed that character and the number of paramagnetic species (transition metal ions: Fe(III), Cu(II), Mn(II) and stable organic radicals) changed upon ozone exposure, depending on the kind of cereal, stress tolerance of particular genotype and the part of grain. The control samples of whole grains and their parts originating from sensitive genotypes contained higher amounts of stable organic radicals (semiquinone, phenoxyl and carbohydrate types) than those from tolerant ones. In embryos of grains from sensitive genotypes their amount increased upon ozone treatment stronger than in embryos from grains of tolerant cultivars. In seed coats and endosperms such relation was not found and the changes in the content of the radicals during ozone application were correlated with the amount of transition metal ions and were more intensive in parts of grains richer in easily oxidized iron species Fe(II), located in inorganic structures. On the contrary, Fe(II) ions situated in embryos were stabilized by organic matrix and did not undergo oxidation by ozone.

Highly efficient conversion of superoxide to oxygen using hydrophilic carbon clusters

Many diseases are associated with oxidative stress, which occurs when the production of reactive oxygen species (ROS) overwhelms the scavenging ability of an organism. Here, we evaluated the carbon nanoparticle antioxidant properties of poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs) by electron paramagnetic resonance (EPR) spectroscopy, oxygen electrode, and spectrophotometric assays. These carbon nanoparticles have 1 equivalent of stable radical and showed superoxide (O2 (•-)) dismutase-like properties yet were inert to nitric oxide (NO(•)) as well as peroxynitrite (ONOO(-)). Thus, PEG-HCCs can act as selective antioxidants that do not require regeneration by enzymes. Our steady-state kinetic assay using KO2 and direct freeze-trap EPR to follow its decay removed the rate-limiting substrate provision, thus enabling determination of the remarkable intrinsic turnover numbers of O2 (•-) to O2 by PEG-HCCs at >20,000 s(-1). The major products of this catalytic turnover are O2 and H2O2, making the PEG-HCCs a biomimetic superoxide dismutase.

Biomarkers of environmental stress in gills of ribbed mussel Aulacomya atra atra (Nuevo Gulf, Northern Patagonia)

In this study, we assessed in gills of native ribbed mussels Aulacomya atra atra from three sites within Nuevo Gulf (Northern Patagonia) several biomarkers such as reactive oxygen species (ROS), lipid radicals (LR), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) and metallothionein (MT). Furthermore, concentrations of main trace metals (Fe, Al, Zn, Cu, Cd and Pb) were quantified in mussel tissue. Results showed significant induction of SOD, GST, MT and MDA, as well as, higher concentration of Fe, Al and Cd in winter than in summer. The high MDA content measured in mussels from Folías Wreck seemed to be caused by the very high levels of Fe that would come from the corrosion of the vessel. Mussels from the control site Punta Cuevas presented the lowest levels of Cd and the highest of Al in winter. Despite positive correlations were found between Al and GST and MT, no spatial differentiation was detected in those biomarkers. On the other hand, MT was only related to Al been most likely influenced by environmental variables than by the trace metals. It has to be highlighted that the relationship detected among water temperature, nutrients and antioxidant responses in gills is probably related to the fact that this tissue is in direct contact with water and it is sensitive to its fluctuations. Taking into account that mussel gill is a tissue actively proliferating and the first target of contaminants present in water, so that changes in its antioxidant system can provide an earlier warning signal than in other tissues.

Assessment of antioxidant responses and trace metal accumulation by digestive gland of ribbed mussel Aulacomya atra atra from Northern Patagonia

Seasonal and spatial variability of trace metal concentrations and of a battery of antioxidant parameters were evaluated in digestive gland of the ribbed mussel Aulacomya atra atra. Fe, Al and Cu accumulated in tissue exhibited maximum values in winter, coinciding partially with the highest labile concentrations of Fe and Cu in sediment. Metals, as other pollutants, are known to influence the oxidative status of organisms and antioxidant enzymes have been often proposed as biomarkers of contaminant effects. Seasonal variations of trace metals did not appear to influence those of biochemical parameters, which generally showed an opposite trend with higher enzymatic activities in summer when trace metal concentrations were lower. Organisms from Punta Cuevas (control site) showed higher induction of reactive oxygen species production than those from both considered impacted sites, suggesting the possibility of some biochemical adaptation in organisms or a higher modulation of environmental and physiological factors on antioxidant responses than levels of trace metals. This study, which is the first in the area in this matter, showed that seasonal variations of potential biomarkers should be incorporated into interpretation of long-term biomonitoring studies in this marine coastal ecosystem.