Unique in vivo applications of spin traps

Versatile Tools for Understanding Electrosynthetic Mechanisms

Electrosynthesis is a popular, green alternative to traditional organic methods. Understanding the mechanisms is not trivial yet is necessary to optimize reaction processes. To this end, a multitude of analytical tools is available to identify and quantitate reaction products and intermediates. The first portion of this review serves as a guide that underscores electrosynthesis fundamentals, including instrumentation, electrode selection, impacts of electrolyte and solvent, cell configuration, and methods of electrosynthesis. Next, the broad base of analytical techniques that aid in mechanism elucidation are covered in detail. These methods are divided into electrochemical, spectroscopic, chromatographic, microscopic, and computational. Technique selection is dependent on predicted reaction pathways and electrogenerated intermediates. Often, a combination of techniques must be utilized to ensure accuracy of the proposed model. To conclude, future prospects that aim to enhance the field are discussed.

Wavelength, dose, skin type and skin model related radical formation in skin

The exposure to sun radiation is indispensable to our health; however, a long-term and high exposure could lead to cell damage, erythema, premature skin aging, and promotion of skin tumors. An underlying pathomechanism is the formation of free radicals which may induce oxidative stress at elevated concentrations. Different skin models, such as porcine-, murine-, human- ex vivo skin, reconstructed human skin (RHS) and human skin in vivo, were investigated during and after irradiation using X- and L-band EPR spectroscopy within different spectral regions (UVC to NIR). The amount of radical formation was quantified with the spin probe PCA and the radical types were measured ex vivo with the spin trap DMPO. The radiation dose influences the types of radicals formed in the skin. While reactive oxygen species (ROS) are always pronounced at low doses, there is an increase in lipid oxygen species (LOS) at high doses. Furthermore, the radical types arise independent from the irradiation wavelength, whereas the general amount of radical formation differs with the irradiation wavelength. Heat pre-stressed porcine skin already starts with higher LOS values. Thus, the radical type ratio might be an indicator of stress and the reversal of ROS/LOS constitutes the point where positive stress turns into negative stress.Compared to light skin types, darker types produce less radicals in the ultraviolet, similar amounts in the visible and higher ones in the infrared spectral region, rendering skin type-specific sun protection a necessity.

Optimizing an Antioxidant TEMPO Copolymer for Reactive Oxygen Species Scavenging and Anti-Inflammatory Effects in Vivo

Oxidative stress is broadly implicated in chronic, inflammatory diseases because it causes protein and lipid damage, cell death, and stimulation of inflammatory signaling. Supplementation of innate antioxidant mechanisms with drugs such as the superoxide dismutase (SOD) mimetic compound 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) is a promising strategy for reducing oxidative stress-driven pathologies. TEMPO is inexpensive to produce and has strong antioxidant activity, but it is limited as a drug due to rapid clearance from the body. It is also challenging to encapsulate into micellar nanoparticles or polymer microparticles, because it is a small, water soluble molecule that does not efficiently load into hydrophobic carrier systems. In this work, we pursued a polymeric form of TEMPO [poly(TEMPO)] to increase its molecular weight with the goal of improving in vivo bioavailability. High density of TEMPO on the poly(TEMPO) backbone limited water solubility and bioactivity of the product, a challenge that was overcome by tuning the density of TEMPO in the polymer by copolymerization with the hydrophilic monomer dimethylacrylamide (DMA). Using this strategy, we formed a series of poly(DMA-co-TEMPO) random copolymers. An optimal composition of 40 mol % TEMPO/60 mol % DMA was identified for water solubility and O2•- scavenging in vitro. In an air pouch model of acute local inflammation, the optimized copolymer outperformed both the free drug and a 100% poly(TEMPO) formulation in O2•- scavenging, retention, and reduction of TNFα levels. Additionally, the optimized copolymer reduced ROS levels after systemic injection in a footpad model of inflammation. These results demonstrate the benefit of polymerizing TEMPO for in vivo efficacy and could lead to a useful antioxidant polymer formulation for next-generation anti-inflammatory treatments.

Solvent Effects on Skin Penetration and Spatial Distribution of the Hydrophilic Nitroxide Spin Probe PCA Investigated by EPR

Oxidative stress occurs in extrinsic skin aging processes and diseases when the enhanced production of free radicals exceeds the homeostatic antioxidant capacity of the skin. The spin probe, 3-(carboxy)-2,2,5,5-tetramethylpyrrolidin-1-oxyl (PCA), is frequently used to study the cutaneous radical production by electron paramagnetic resonance (EPR) spectroscopy. This approach requires delivering PCA into the skin, yet solvent effects on the skin penetration and spatial distribution of PCA have not been thoroughly investigated. Three solvents of ethanol, phosphate-buffered saline (PBS) and ethanol-PBS (1:1) were studied. For both human and porcine skin ex vivo, the amount of PCA in the stratum corneum (SC) was the lowest when using ethanol and very similar for PBS and ethanol-PBS. The highest amount of PCA in the viable skin layers was detected for ethanol-PBS, yet it only took up less than 5% of the total amount. The majority of PCA was localized in the SC, among which PCA with high mobility was predominantly distributed in the hydrophilic microenvironment of corneocytes and PCA with lower mobility was mainly in the less hydrophilic microenvironment of intercellular skin lipids. A higher ethanol concentration in the solvent could improve the distribution of PCA in the hydrophilic microenvironments of the SC. The results suggest that ethanol-PBS (1:1) is best-suited for delivering most PCA deep into the skin. This work enhances the understanding of solvent effects on the skin penetration and distribution of PCA and supports the utilization of PCA in studying cutaneous radical production.

Heterogeneity of Metabolic Defects in Type 2 Diabetes and Its Relation to Reactive Oxygen Species and Alterations in Beta-Cell Mass

Type 2 diabetes (T2D) is a complex and heterogeneous disease which affects millions of people worldwide. The classification of diabetes is at an interesting turning point and there have been several recent reports on sub-classification of T2D based on phenotypical and metabolic characteristics. An important, and perhaps so far underestimated, factor in the pathophysiology of T2D is the role of oxidative stress and reactive oxygen species (ROS). There are multiple pathways for excessive ROS formation in T2D and in addition, beta-cells have an inherent deficit in the capacity to cope with oxidative stress. ROS formation could be causal, but also contribute to a large number of the metabolic defects in T2D, including beta-cell dysfunction and loss. Currently, our knowledge on beta-cell mass is limited to autopsy studies and based on comparisons with healthy controls. The combined evidence suggests that beta-cell mass is unaltered at onset of T2D but that it declines progressively. In order to better understand the pathophysiology of T2D, to identify and evaluate novel treatments, there is a need for in vivo techniques able to quantify beta-cell mass. Positron emission tomography holds great potential for this purpose and can in addition map metabolic defects, including ROS activity, in specific tissue compartments. In this review, we highlight the different phenotypical features of T2D and how metabolic defects impact oxidative stress and ROS formation. In addition, we review the literature on alterations of beta-cell mass in T2D and discuss potential techniques to assess beta-cell mass and metabolic defects in vivo.

Synthesis and evaluation of 13C-labeled 5-5-dimethyl-1-pyrroline-N-oxide aimed at in vivo detection of reactive oxygen species using hyperpolarized 13C-MRI

Effective means to identify the role of reactive oxygen species (ROS) mediating several diseases including cancer, ischemic heart disease, stroke, Alzheimer's and other inflammatory conditions in in vivo models would be useful. The cyclic nitrone 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) is a spin trap frequently used to detect free radicals in vitro using Electron Paramagnetic Resonance (EPR) spectroscopy. In this study, we synthesized ¹³C-labeled DMPO for hyperpolarization by dynamic nuclear polarization, in which ¹³C NMR signal increases more than 10,000-fold. This allows in vivo ¹³C MRI to investigate the feasibility of in vivo ROS detection by the ¹³C-MRI. DMPO was ¹³C-labeled at C5 position, and deuterated to prolong the T₁ relaxation time. The overall yield achieved for 5-¹³C-DMPO-d₉ was 15%. Hyperpolarized 5-¹³C-DMPO-d₉ provided a single peak at 76 ppm in the ¹³C-spectrum, and the T₁ was 60 s in phosphate buffer making it optimal for in vivo ¹³C MRI. The buffered solution of hyperpolarized 5-¹³C-DMPO-d₉ was injected into a mouse placed in a 3 T scanner, and ¹³C-spectra were acquired every 1 s. In vivo studies showed the signal of 5-¹³C-DMPO-d₉ was detected in the mouse, and the T₁ decay of ¹³C signal of hyperpolarized 5-¹³C-DMPO-d₉ was 29 s. ¹³C-chemical shift imaging revealed that 5-¹³C-DMPO-d₉ was distributed throughout the body in a minute after the intravenous injection. A strong signal of 5-¹³C-DMPO-d₉ was detected in heart/lung and kidney, whereas the signal in liver was small compared to other organs. The results indicate hyperpolarized 5-¹³C-DMPO-d₉ provided sufficient ¹³C signal to be detected in the mouse in several organs, and can be used to detect ROS in vivo.

In Vivo and In Situ Detection of Macromolecular Free Radicals Using Immuno-Spin Trapping and Molecular Magnetic Resonance Imaging

SIGNIFICANCE

In vivo free radical imaging in preclinical models of disease has become a reality. Free radicals have traditionally been characterized by electron spin resonance (ESR) or electron paramagnetic resonance (EPR) spectroscopy coupled with spin trapping. The disadvantage of the ESR/EPR approach is that spin adducts are short-lived due to biological reductive and/or oxidative processes. Immuno-spin trapping (IST) involves the use of an antibody that recognizes macromolecular 5,5-dimethyl-pyrroline-N-oxide (DMPO) spin adducts (anti-DMPO antibody), regardless of the oxidative/reductive state of trapped radical adducts. Recent Advances: The IST approach has been extended to an in vivo application that combines IST with molecular magnetic resonance imaging (mMRI). This combined IST-mMRI approach involves the use of a spin-trapping agent, DMPO, to trap free radicals in disease models, and administration of an mMRI probe, an anti-DMPO probe, which combines an antibody against DMPO-radical adducts and an MRI contrast agent, resulting in targeted free radical adduct detection.

CRITICAL ISSUES

The combined IST-mMRI approach has been used in several rodent disease models, including diabetes, amyotrophic lateral sclerosis (ALS), gliomas, and septic encephalopathy. The advantage of this approach is that heterogeneous levels of trapped free radicals can be detected directly in vivo and in situ to pin point where free radicals are formed in different tissues.

FUTURE DIRECTIONS

The approach can also be used to assess therapeutic agents that are either free radical scavengers or generate free radicals. Smaller probe constructs and radical identification approaches are being considered. The focus of this review is on the different applications that have been studied, advantages and limitations, and future directions. Antioxid. Redox Signal. 28, 1404-1415.

Detection of Nitric Oxide by Electron Paramagnetic Resonance Spectroscopy: Spin-Trapping with Iron-Dithiocarbamates

Electron paramagnetic resonance (EPR) spectroscopy is the ideal methodology to identify radicals (detection and characterization of molecular structure) and to study their kinetics, in both simple and complex biological systems. The very low concentration and short life-time of NO and of many other radicals do not favor its direct detection and spin-traps are needed to produce a new and persistent radical that can be subsequently detected by EPR spectroscopy.In this chapter, we present the basic concepts of EPR spectroscopy and of some spin-trapping methodologies to study NO. The "strengths and weaknesses" of iron-dithiocarbamates utilization, the NO traps of choice for the authors, are thoroughly discussed and a detailed description of the method to quantify the NO formation by molybdoenzymes is provided.

Physiological and pathophysiological reactive oxygen species as probed by EPR spectroscopy: the underutilized research window on muscle ageing

Reactive oxygen and nitrogen species (ROS and RNS) play crucial roles in triggering, mediating and regulating physiological and pathophysiological signal transduction pathways within the cell. Within the cell, ROS efflux is firmly controlled both spatially and temporally, making the study of ROS dynamics a challenging task. Different approaches have been developed for ROS assessment; however, many of these assays are not capable of direct identification or determination of subcellular localization of different ROS. Here we highlight electron paramagnetic resonance (EPR) spectroscopy as a powerful technique that is uniquely capable of addressing questions on ROS dynamics in different biological specimens and cellular compartments. Due to their critical importance in muscle functions and dysfunction, we discuss in some detail spin trapping of various ROS and focus on EPR detection of nitric oxide before highlighting how EPR can be utilized to probe biophysical characteristics of the environment surrounding a given stable radical. Despite the demonstrated ability of EPR spectroscopy to provide unique information on the identity, quantity, dynamics and environment of radical species, its applications in the field of muscle physiology, fatiguing and ageing are disproportionately infrequent. While reviewing the limited examples of successful EPR applications in muscle biology we conclude that the field would greatly benefit from more studies exploring ROS sources and kinetics by spin trapping, protein dynamics by site-directed spin labelling, and membrane dynamics and global redox changes by spin probing EPR approaches.

Catalase Expression Is Modulated by Vancomycin and Ciprofloxacin and Influences the Formation of Free Radicals in Staphylococcus aureus Cultures

Detection of free radicals in biological systems is challenging due to their short half-lives. We have applied electron spin resonance (ESR) spectroscopy combined with spin traps using the probes PBN (N-tert-butyl-α-phenylnitrone) and DMPO (5,5-dimethyl-1-pyrroline N-oxide) to assess free radical formation in the human pathogen Staphylococcus aureus treated with a bactericidal antibiotic, vancomycin or ciprofloxacin. While we were unable to detect ESR signals in bacterial cells, hydroxyl radicals were observed in the supernatant of bacterial cell cultures. Surprisingly, the strongest signal was detected in broth medium without bacterial cells present and it was mitigated by iron chelation or by addition of catalase, which catalyzes the decomposition of hydrogen peroxide to water and oxygen. This suggests that the signal originates from hydroxyl radicals formed by the Fenton reaction, in which iron is oxidized by hydrogen peroxide. Previously, hydroxyl radicals have been proposed to be generated within bacterial cells in response to bactericidal antibiotics. We found that when S. aureus was exposed to vancomycin or ciprofloxacin, hydroxyl radical formation in the broth was indeed increased compared to the level seen with untreated bacterial cells. However, S. aureus cells express catalase, and the antibiotic-mediated increase in hydroxyl radical formation was correlated with reduced katA expression and catalase activity in the presence of either antibiotic. Therefore, our results show that in S. aureus, bactericidal antibiotics modulate catalase expression, which in turn influences the formation of free radicals in the surrounding broth medium. If similar regulation is found in other bacterial species, it might explain why bactericidal antibiotics are perceived as inducing formation of free radicals.

GlxA is a new structural member of the radical copper oxidase family and is required for glycan deposition at hyphal tips and morphogenesis of Streptomyces lividans

Streptomyces lividans displays a distinct dependence on copper to fully initiate morphological development. Evidence has accumulated to implicate the participation of an extracytoplasmic cuproenzyme in morphogenesis. In the present study, we show that GlxA fulfils all criteria to be that cuproenzyme. GlxA is membrane associated and has an active site consisting of a mononuclear copper and a cross-linked Y-C cofactor. The domain organization of the tertiary structure defines GlxA as a new structural member of the mono-copper oxidase family, with copper co-ordination geometry similar to, but spectroscopically distinct from fungal galactose oxidase (Gox). EPR spectroscopy reveals that the oxidation of cupric GlxA generates a protein radical residing on the Y-C cross-link. A variety of canonical Gox substrates (including D-galactose) were tested but none were readily turned over by GlxA. A glxA null-mutant leads to loss of glycan accumulation at hyphal tips and consequently a drastically changed morphology both on solid substrates and in liquid-grown environments, a scenario similarly observed in the absence of the neighbouring glycan synthase CslA (cellulase synthase-like protein). In addition the glxA mutant has lost the stimulation of development by copper, supporting a model whereby the enzymatic action of GlxA on the glycan is required for development and morphology. From a biotechnology perspective, the open mycelium morphology observed with the glxA mutant in submerged culture has implications for use as an enzyme production host.

Room-Temperature Electron Spin Relaxation of Triarylmethyl Radicals at the X- and Q-Bands

Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long relaxation of trityls at room temperature in liquid solutions makes them a promising alternative for traditional nitroxides. In this work we have synthesized a series of TAMs including perdeuterated Finland trityl (D36 form), mono-, di-, and triester derivatives of Finland-D36 trityl, the deuterated form of OX63, the dodeca-n-butyl homologue of Finland trityl, and triamide derivatives of Finland trityl with primary and secondary amines attached. We have studied room-temperature relaxation properties of these TAMs in liquids using pulsed electron paramagnetic resonance (EPR) at two microwave frequency bands. We have found the clear dependence of phase memory time (Tm ∼ T2) on the magnetic field: room-temperature Tm values are ∼1.5-2.5 times smaller at the Q-band (34 GHz, 1.2 T) than at the X-band (9 GHz, 0.3 T). This trend is ascribed to the contribution from g-anisotropy that is negligible at lower magnetic fields but comes into play at the Q-band. In agreement with this, the difference between T1 and Tm becomes more pronounced at the Q-band than at the X-band due to increased contributions from incomplete motional averaging of g-anisotropy. Linear dependence of (1/Tm - 1/T1) on viscosity implies that g-anisotropy is modulated by rotational motion of the trityl radical. On the basis of the analysis of previous data and results of the present work, we conclude that, in the general situation where the spin label is at least partly mobile, the X-band is most suitable for application of trityls for room-temperature pulsed EPR distance measurements.

Detection of superoxide production in stimulated and unstimulated living cells using new cyclic nitrone spin traps

Reactive oxygen species (ROS), including superoxide anion and hydrogen peroxide (H2O2), have a diverse array of physiological and pathological effects within living cells depending on the extent, timing, and location of their production. For measuring ROS production in cells, the ESR spin trapping technique using cyclic nitrones distinguishes itself from other methods by its specificity for superoxide and hydroxyl radical. However, several drawbacks, such as the low spin trapping rate and the spontaneous and cell-enhanced decomposition of the spin adducts to ESR-silent products, limit the application of this method to biological systems. Recently, new cyclic nitrones bearing a triphenylphosphonium (Mito-DIPPMPO) or a permethylated β-cyclodextrin moiety (CD-DIPPMPO) have been synthesized and their spin adducts demonstrated increased stability in buffer. In this study, a comparison of the spin trapping efficiency of these new compounds with commonly used cyclic nitrone spin traps, i.e., 5,5-dimethyl-1-pyrroline N-oxide (DMPO), and analogs BMPO, DEPMPO, and DIPPMPO, was performed on RAW 264.7 macrophages stimulated with phorbol 12-myristate 13-acetate. Our results show that Mito-DIPPMPO and CD-DIPPMPO enable a higher detection of superoxide adduct, with a low (if any) amount of hydroxyl adduct. CD-DIPPMPO, especially, appears to be a superior spin trap for extracellular superoxide detection in living macrophages, allowing measurement of superoxide production in unstimulated cells for the first time. The main rationale put forward for this extreme sensitivity is that the extracellular localization of the spin trap prevents the reduction of the spin adducts by ascorbic acid and glutathione within cells.

WITHDRAWN: Superoxide generation in different brain regions of rats during normoxia and hypoxia-reoxygenation

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.neures.2012.10.010. The duplicate article has therefore been withdrawn.

Superoxide generation in different brain regions of rats during normoxia and hypoxia-reoxygenation

The superoxide-dependent chemiluminescent intensity in different brain regions was examined in ex vivo tissue slices of rat brain during normoxia and hypoxia-reoxygenation with lucigenin. The chemiluminescent intensity increased during reoxygenation after hypoxic treatment. There was a higher level of chemiluminescent intensity in the hippocampus during normoxia, and a lower level in the white matter during normoxia and hypoxia-reoxygenation. A weak correlation was found between the chemiluminescent intensity and the glucose uptake rate during normoxia. Then we examined whether hypoxic strength correlates to superoxide generation. The chemiluminescent intensity increased in a hypoxic strength-dependent manner. The generation mechanism of superoxide was examined using carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler, genipin, an inhibitor for uncoupling protein-2, alloprinol, a xanthine oxidase inhibitor, or apocynin, an NADPH oxidase inhibitor. The chemiluminescent signal was significantly inhibited by CCCP under normoxic condition and enhanced by genipin during normoxia and hypoxia-reoxygenation, but not by allopurinol or apocynin. These results suggest that superoxide generation is high in the hippocampus during normoxia and low in the white matter during normoxia and hypoxia-reoxygenation, superoxide generation in the hypoxia-reoxygenation brain correlates with the strength of hypoxia influenced by oxygen delivery, and mitochondrion is the major sites of intracellular superoxide generation.

Redox modulation of the DNA damage response

Lesions to DNA trigger the DNA-damage response (DDR), a complex, multi-branched cell-intrinsic process targeted to DNA repair, or elimination of the damaged cells by apoptosis. DDR aims at reducing permanence of mutated cells, decreasing the risk of tumor development: the more stringent the response, the lower the likelihood that sub-lethally damaged, unrepaired cells survive and proliferate. Accordingly, leakage often occurs in tumor cells with compromised DDR, accumulating mutations and accelerating tumor progression. Oxidations mediate DNA damage upon different insults such as UV, X and γ radiation, pollutants, poisons, or endogenous disequilibria, producing different types of lesions that trigger DDR, which can be alleviated by antioxidants. But reactive oxygen species (ROS), and the enzymes involved in their production or scavenging, also participate in DDR signaling, modulating the activity of key enzymes, and regulating the stringency of DDR. Accordingly, antioxidant enzymes such as superoxide dismutase play intimate and complex roles in tumor development, exceeding the basal roles of preventing the initial DNA damage. Likewise, it is emerging that dietary antioxidants help controlling tumor onset and progression by preventing DNA damage and by acting on cell cycle checkpoints, opening a novel and promising frontier to anticancer therapy.

Post-trapping derivatization of radical-derived EPR-silent adducts: application to free radical detection by HPLC/UV in chemical, biochemical, and biological systems and comparison with EPR spectroscopy

Free radicals are conventionally detected by electron paramagnetic resonance (EPR) spectroscopy after being trapped as spin adducts. Albeit this technique has demonstrated utmost efficacy in studying free radicals, its application to biological settings is intrinsically hampered by the inevitable bioreduction of radical-derived paramagnetic adducts. Herein, we describe a reliable technique to detect and quantify free radical metabolites, wherein reduced alkyl- and phenyl-5,5-dimethyl-1-pyrroline N-oxide (DMPO) adducts are converted into ultrastable N-naphthoate esters. To mimic the ubiquitous in vivo microenvironment, bioreductants, exogenous thiols, and sodium borohydride were studied. Nitroxyl reduction was confirmed using EPR and triphenyltetrazolium chloride. The formation of the N-naphthoyloxy derivatives was established by liquid chromatography/mass spectrometry (LC/MS). The derivatives were chromatographed using a binary eluent. HPLC and internal standards were synthesized using Grignard addition. The labeled DMPO adduct is (1) fluorescent, (2) stable as opposed to nitroxyl radical adducts, (3) biologically relevant, and (4) excellently chromatographed. Applications encompassed chemical, biochemical, and biological model systems generating C-centered radicals. Different levels of phenyl radicals produced in situ from whole blood were successfully determined. The method is readily applicable to the detection of hydroxyl radical. Analogously, DMPO, the spin trap, could be detected with extreme sensitivity suitable for in vivo applications. The developed method proved to be a viable alternative to EPR, where for the first time the reductive loss of paramagnetic signals of DMPO-trapped free radicals is transformed into fluorescence emission. We believe the proposed methodology could represent a valuable tool to probe free radical metabolites in vivo using DMPO, the least toxic spin trap.

TiO2 nanoparticles are phototoxic to marine phytoplankton

Nanoparticulate titanium dioxide (TiO₂) is highly photoactive, and its function as a photocatalyst drives much of the application demand for TiO₂. Because TiO₂ generates reactive oxygen species (ROS) when exposed to ultraviolet radiation (UVR), nanoparticulate TiO₂ has been used in antibacterial coatings and wastewater disinfection, and has been investigated as an anti-cancer agent. Oxidative stress mediated by photoactive TiO₂ is the likely mechanism of its toxicity, and experiments demonstrating cytotoxicity of TiO₂ have used exposure to strong artificial sources of ultraviolet radiation (UVR). In vivo tests of TiO₂ toxicity with aquatic organisms have typically shown low toxicity, and results across studies have been variable. No work has demonstrated that photoactivity causes environmental toxicity of TiO₂ under natural levels of UVR. Here we show that relatively low levels of ultraviolet light, consistent with those found in nature, can induce toxicity of TiO₂ nanoparticles to marine phytoplankton, the most important primary producers on Earth. No effect of TiO₂ on phytoplankton was found in treatments where UV light was blocked. Under low intensity UVR, ROS in seawater increased with increasing nano-TiO₂ concentration. These increases may lead to increased overall oxidative stress in seawater contaminated by TiO₂, and cause decreased resiliency of marine ecosystems. Phototoxicity must be considered when evaluating environmental impacts of nanomaterials, many of which are photoactive.

Production of free radicals and oxygen consumption by primary equine endothelial cells during anoxia-reoxygenation

The endothelium plays an active role in ischemia/reperfusion injuries. Herein, we report the effect of a single or successive cycles of anoxia/reoxygenation (A/R) on the mitochondrial respiratory function of equine endothelial cells (cultured from carotids) monitored by high resolution oxymetry, and on their production of reactive oxygen species (ROS). ROS were measured by electron paramagnetic resonance (ESR) using POBN and DMPO spin traps, and by gas chromatography (GC) of ethylene released by ROS-induced α-keto-γ-(methylthio)butyric acid (KMB) oxidation. The oxygen consumption significantly decreased with the number of A/R cycles, and POBN-ESR spectra were specific of adducts formed in the cells from superoxide anion. After a one-hour A/R cycle, high intensity DMPO-ESR spectra were observed and assigned to superoxide anion trapping; the GC results confirmed an important production of ROS compared to normoxic cells. These results show that A/R induces mitochondrial alterations in endothelial cells, and strongly stimulates their oxidative activity as demonstrated by ESR and GC methods.

Electron paramagnetic resonance spectroscopy in radiation research: Current status and perspectives

Exposure to radiation leads to a number of health-related malfunctions. Ionizing radiation is more harmful than non-ionizing radiation, as it causes both direct and indirect effects. Irradiation with ionizing radiation results in free radical-induced oxidative stress. Free radical-mediated oxidative stress has been implicated in a plethora of diseased states, including cancer, arthritis, aging, Parkinson's disease, and so on. Electron Paramagnetic Resonance (EPR) spectroscopy has various applications to measure free radicals, in radiation research. Free radicals disintegrate immediately in aqueous environment. Free radicals can be detected indirectly by the EPR spin trapping technique in which these forms stabilize the radical adduct and produce characteristic EPR spectra for specific radicals. Ionizing radiation-induced free radicals in calcified tissues, for example, teeth, bone, and fingernail, can be detected directly by EPR spectroscopy, due to their extended stability. Various applications of EPR in radiation research studies are discussed in this review.

Acute effect of nitric oxide supplement on blood nitrate/nitrite and hemodynamic variables in resistance trained men

Nitric oxide dietary supplements are extremely popular within the sport and bodybuilding community. Most products contain l-arginine, for which there is no direct evidence that oral L-arginine increases circulating nitric oxide or blood flow. A new molecule (2-[nitrooxy]thyl 2-amino-3-methylbutanoate) is being marketed as a sport supplement for purposes of delivering "real nitric oxide" to the circulation. In the present study, we measured the acute effects of this supplement on blood nitrate/nitrite and hemodynamic variables. Ten resistance trained men (26 ± 4 years old; 8 ± 6 years of resistance exercise training) reported to the laboratory in random order after a 10-hour overnight fast on 2 occasions separated by 1 week and were provided the supplement (2-[nitrooxy]ethyl 2-amino-3-methylbutanoate) or placebo. Heart rate and blood pressure were recorded, and venous blood samples were collected before and at 5, 15, 30, and 60 minutes after complete breakdown of the supplement (5 minutes post intake) or placebo. Blood samples were assayed for plasma nitrate/nitrite. No interaction (p = 0.99), condition (p = 0.18), or time (p = 0.98) effects were noted for plasma nitrate/nitrite, with values remaining nearly identical across time for placebo (∼27 μmol·L(-1)) and increasing a maximum of ∼6.7% (from 32.9 to 35.1 μmol·L(-1)) at the 15-minute collection period for the supplement. In regards to hemodynamic variables, no interaction, condition, or time effects were noted for heart rate, systolic, or diastolic blood pressure (p > 0.05), with values near identical between conditions and virtually unchanged across time. These findings indicate that 2-(nitrooxy)ethyl 2-amino-3-methylbutanoate has a small effect on increasing circulating nitrate/nitrite and does not cause any change in hemodynamic variables within the 1 hour postingestion period in a sample of resistance trained men.

Sedentary aging increases resting and exercise-induced intramuscular free radical formation

Mitochondrial free radical formation has been implicated as a potential mechanism underlying degenerative senescence, although human data are lacking. Therefore, the present study was designed to examine if resting and exercise-induced intramuscular free radical-mediated lipid peroxidation is indeed increased across the spectrum of sedentary aging. Biopsies were obtained from the vastus lateralis in six young (26 + or - 6 yr) and six aged (71 + or - 6 yr) sedentary males at rest and after maximal knee extensor exercise. Aged tissue exhibited greater (P < 0.05 vs. the young group) electron paramagnetic resonance signal intensity of the mitochondrial ubisemiquinone radical both at rest (+138 + or - 62%) and during exercise (+143 + or - 40%), and this was further complemented by a greater increase in alpha-phenyl-tert-butylnitrone adducts identified as a combination of lipid-derived alkoxyl-alkyl radicals (+295 + or - 96% and +298 + or - 120%). Lipid hydroperoxides were also elevated at rest (0.190 + or - 0.169 vs. 0.148 + or - 0.071 nmol/mg total protein) and during exercise (0.567 + or - 0.259 vs. 0.320 + or - 0.263 nmol/mg total protein) despite a more marked depletion of ascorbate and uptake of alpha/beta-carotene, retinol, and lycopene (P < 0.05 vs. the young group). The impact of senescence was especially apparent when oxidative stress biomarkers were expressed relative to the age-related decline in mitochondrial volume density and absolute power output at maximal exercise. In conclusion, these findings confirm that intramuscular free radical-mediated lipid peroxidation is elevated at rest and during acute exercise in aged humans.

Plastid alternative oxidase (PTOX) promotes oxidative stress when overexpressed in tobacco

Photoinhibition and production of reactive oxygen species were studied in tobacco plants overexpressing the plastid terminal oxidase (PTOX). In high light, these plants was more susceptible to photoinhibition than wild-type plants. Also oxygen-evolving activity of isolated thylakoid membranes from the PTOX-overexpressing plants was more strongly inhibited in high light than in thylakoids from wild-type plants. In contrast in low light, in the PTOX overexpressor, the thylakoids were protected against photoinhibition while in wild type they were significantly damaged. The production of superoxide and hydroxyl radicals was shown by EPR spin-trapping techniques in the different samples. Superoxide and hydroxyl radical production was stimulated in the overexpressor. Two-thirds of the superoxide production was maintained in the presence of DNP-INT, an inhibitor of the cytochrome b(6)f complex. No increase of the SOD content was observed in the overexpressor compared with the wild type. We propose that superoxide is produced by PTOX in a side reaction and that PTOX can only act as a safety valve under stress conditions when the generated superoxide is detoxified by an efficient antioxidant system.

ExogenousN-linoleoyl tyrosine marker as a tool for the characterization of cellular oxidative stress in macrophages

Oxidative stress and its resultant products continue to attract investigators. Numerous endogenous substances have been suggested as potential markers for the identification of oxidative stress in tissues and organisms. In this study, we present a novel concept whereby an exogenous marker is designed and synthesized for the characterization of oxidative stress. The designed marker is constructed from tyrosine (Tyr) and linoleic acid (LA), which are attached covalently to form N-linoleoyl tyrosine (N-LT). Each of the two components (Tyr and LA) is known to be easily oxidized upon exposure to different types of reactive species. Combining the two allows their distinction from the endogenous Tyr and LA in the tested biological samples. The ability of the N-LT marker to characterize oxidative stress in macrophage cell lines was first studied using different types of ROS/RNS. N-LT was found to interact with macrophages, binding to the cell membrane. Upon treatment of J-774 A.1 macrophages with N-LT (40 microM) and with various oxidants; HOCl (0.2, 0.4 mM), copper ions (20 microM), SIN-1 (0.1, 1.0 mM), specific oxidized N-LT (Ox-N-LT) products were formed, depending on the type of oxidant used. Exposing cells to HOCl (0.2 mM) resulted in exclusive attack of the LA residue of N-LT, preferentially forming an adduct of HOCl to the LA double bond (N-L(HOCl)T, 4.3%). In contrast, when SIN-1 (0.1 mM) was applied as the oxidant, the Tyr moiety of N-LT was most reactive, yielding a nitration product of the Tyr aromatic ring (N-LT(NO(2)), 1.8%). Similar N-LT oxidation in cell-free systems yielded a significantly higher content of Ox-N-LT (10.8% N-L(HOCl)T, 7% N-LT(NO(2)). The designed marker was then tested with peritoneal macrophages taken from atherosclerotic apolipoprotein-deficient (E(0)) mice showing specific and selective oxidation of N-LT to yield N-LT-hydroperoxide (1.9% N-L(OOH)T), at significantly higher levels than resulted from similar experiments using peritoneal macrophages harvested from control BalbC mice (0.0% N-L(OOH)T). In contrast, the differences in N-L(epoxy)T level between BalbC and E(0) mice were not significant using both types of peritoneal macrophages (E(0) and BalbC), suggesting that N-L(OOH)T is characteristic of the atherosclerotic state. Thus, we show that the designed marker is sufficiently sensitive to detect oxidative stress imposed on cells and cell-free systems and to react selectively with the various ROS/RNS induced. Such a marker may be useful for characterizing oxidative stress in general, and possibly also in oxidative-stress-associated diseases.

Spinnokinetic Analyses of Blood Disposition and Biliary Excretion of Nitric Oxide (NO)-Fe(II)-N-(Dithiocarboxy)sarcosine Complex in Rats: BCM-ESR and BEM-ESR Studies

Nitric oxide (NO) is well known to have a wide variety of biological and physiological functions in animals. On the basis of the fact that Fe(II)-dithiocarbamates react with NO, a Fe(II)-N-(dithiocarboxy)sarcosine complex (Fe(II)-DTCS) was proposed as a trapping agent for endogenous NO. However, quantitative pharmacokinetic investigation for NO-Fe(II)-dithiocarbamate complexes in experimental animals has been quite limited. This paper describes the results on the quantitative pharmacokinetic features of a NO-Fe(II)-N-DTCS in both the blood and bile of rats following intravenous (i.v.) administration of the complex. For this purpose, we applied two in vivo methods, i.e. (1) in vivo blood circulation monitoring-electron spin resonance (BCM-ESR) which previously developed, and (2) in vivo biliary excretion monitoring-electron spin resonance (BEM-ESR). We monitored real-time ESR signals due to nitrosyl-iron species in the circulating blood and bile flow. The ESR signal due to NO-Fe(II)-DTCS was stable in biological systems such as the fresh blood and bile. In in vivo BCM- and BEM-ESR, the pharmacokinetic parameters were calculated on the basis of the two-compartment and hepatobiliary transport models. The studies also revealed that the compound is widely distributed in the peripheral organs and partially excreted into the bile. We named a kinetic method to follow spin concentrations as spinnokinetics and this method will be useful for detecting and quantifying the endogenously generated NO in Fe(II)-DTCS administered animals.

Use of conventional and -omics based methods for health claims of dietary antioxidants: a critical overview

This article describes the principles and limitations of methods used to investigate reactive oxygen species (ROS) protective properties of dietary constituents and is aimed at providing a better understanding of the requirements for science based health claims of antioxidant (AO) effects of foods. A number of currently used biochemical measurements aimed of determining the total antioxidant capacity and oxidised lipids and proteins are carried out under unphysiological conditions and are prone to artefact formation. Probably the most reliable approaches are measurements of isoprostanes as a parameter of lipid peroxidation and determination of oxidative DNA damage. Also the design of the experimental models has a strong impact on the reliability of AO studies: the common strategy is the identification of AO by in vitro screening with cell lines. This approach is based on the assumption that protection towards ROS is due to scavenging, but recent findings indicate that activation of transcription factors which regulate genes involved in antioxidant defence plays a key role in the mode of action of AO. These processes are not adequately represented in cell lines. Another shortcoming of in vitro experiments is that AO are metabolised in vivo and that most cell lines are lacking enzymes which catalyse these reactions. Compounds with large molecular configurations (chlorophylls, anthocyans and polyphenolics) are potent AO in vitro, but weak or no effects were observed in animal/human studies with realistic doses as they are poorly absorbed. The development of -omics approaches will improve the scientific basis for health claims. The evaluation of results from microarray and proteomics studies shows that it is not possible to establish a general signature of alterations of transcription and protein patterns by AO. However, it was shown that alterations of gene expression and protein levels caused by experimentally induced oxidative stress and ROS related diseases can be normalised by dietary AO.

Characterization of oxidative stress in blood from diabetic vs. hypercholesterolaemic patients, using a novel synthesized marker

In the present study, we extend our novel concept of designing and using exogenous markers for the characterization of oxidative stress (OS) and OS-associated diseases. The aim was to use such a synthetic compound as a tool for studying OS in blood from diabetic and hypercholesterolaemic (Hc) patients. The marker used N-linoleoyl tyrosine (LT) was constructed from tyrosine and linoleic acid (LA); both components are known to be easily oxidized upon exposure to different types of reactive oxygen/nitrogen species (ROS/RNS), and to generate specific oxidized products, depending on the type of oxidants present in vivo. Using the LT probe, we showed that the ratios of oxidized LT to total LT (Ox-LT/LT) is significantly higher in blood samples obtained from diabetic patients, than in Hc patients or healthy control subjects. LC/MS analysis revealed that blood from diabetic patients oxidizes the marker with predominant formation of Ox-LT hydroperoxide (LT-OOH) and epoxide (epoxy-LT), where the LA moiety is oxidized to hydroperoxide and to epoxide, respectively. Analysis of oxysterol levels in these samples (GC/MS) revealed that the blood of both diabetic and Hc patients contained significantly more oxysterols than blood of control subjects. Consumption of pomegranate juice by diabetic patients for 3 months suppressed their blood capacity to oxidize the LT and similarly also reduced their blood oxysterol/total cholesterol ratio by 93%. The use of an exogenous marker to characterize OS in blood samples yields important information on the extent of OS, and can provide a fingerprint for the early identification of different pathological conditions associated with OS.

In vivo quantification of oxygen-free radical release in experimental pancreas transplantation

Reactive oxygen species (ROS) were drawn to the attention in the setting of organ transplantation when the 'injury hypothesis' postulated a link between oxidative stress and the activation of the innate immunity of the recipient. While the occurrence of ROS during organ transplantation is undoubted, their onset and magnitude remain largely unknown. We therefore measured ROS using a novel cyclic hydroxylamine spin probe CMH (1-hydroxy-3- methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine) during syngeneic experimental pancreas transplantation in rats in vivo. Organs were subjected to two different cold preservation methods [University of Wisconsin preservation solution (UW) or normal saline] for 18 h. During the first 90 min of reperfusion, samples were collected and analysed using electron paramagnetic resonance signalling. Isolated blood-free perfused organs (IPO) were used for comparison. Analysis showed that it is feasible to detect ROS using CMH spin probes. While IPO organs displayed a very early ROS release, there was no ROS increase in the UW preserved group compared to NaCl. These findings were in line with conventional markers of organ damage such as serum lactate, glucose, potassium as well as tissue ATP levels. CMH spin probes might become a useful tool for the in vivo animal testing of antioxidative substances in models of solid organ transplantation.

Tocopherols and tocotrienols in membranes: a critical review

The familiar role of tocols (tocopherols and tocotrienols) as lipid-soluble chain-terminating inhibitors of lipid peroxidation is currently in the midst of a reinterpretation. New biological activities have been described for tocols that apparently are not dependent on their well-established antioxidant behaviour. These activities could well be real, but there remain large gaps in our understanding of the behaviour of tocols in membranes, especially when it comes to the alpha-, beta-, gamma-, delta-chroman methylation patterns and the seemingly special nature of tocotrienols. It is inappropriate to make conclusions and develop models based on in vivo (or cell culture) results with reference to in vitro measurements of antioxidant activity. When present in biological membranes, tocols will experience a large variation in the local composition of phospholipids and the presence of neutral lipids such as cholesterol, both of which would be expected to change the efficiency of antioxidant action. It is likely that tocols are not homogeneously dispersed in a membrane, but it is still not known whether any specific combination of lipid head group and acyl chains are conferred special protection from peroxidation, nor do we currently appreciate the structural role that tocols play in membranes. Tocols may enhance curvature stress or counteract similar stresses generated by other lipids such as lysolipids. This review will outline what is known about the location and behaviour of tocols in phospholipid bilayers. We will draw mainly from the biophysical literature, but will attempt to extend the discussion to biologically relevant phenomena when appropriate. We hope that it will assist researchers when designing new experiments and when critically assessing the results, in turn providing a more thorough understanding of the biochemistry of tocols.

Evaluation of Copper(II) Eriochrome Cyanine R (ECR) Complex Immobilized in Anion Exchange Membrane as a Potential Nitric Oxide Optical Sensor

The immobilization of the copper(ii) complex of Eriochrome cyanine R (Cu(ECR)2) in anion exchange membranes was investigated in the development of an optical sensor for nitric oxide (NO) gas. The change in the absorbance spectrum of Cu(ECR)2 membranes was monitored at 445 nm on exposure to NO gas and a steady-state response was obtained following a 400 s exposure time. This response was highly linear (r2 = 0.996) up to 6 ppm NO and the detection limit was calculated to be 0.848 ppm (~28.28 μM in solution). This response was 4.7 times more sensitive to changing NO gas concentrations (0–6 ppm) compared with that of Cu(ECR)2 immobilized in silicone rubber films. This response was fully reversible by resubmersion of the membranes in copper(ii) solution following NO exposure and this reversibility was extremely reproducible (0.81%, relative standard deviation, n = 3). These anion exchange membranes were more selective to NO gas rather than O2 (80:1), NO2 (3:1), and CO (7:1) and these gases were shown not to interfere with the reaction of Cu-ECR membranes with NO itself.

Dynamic changes in parameters of redox balance after mild heat stress in aged laying hens (Gallus gallus domesticus)

In order to evaluate the metabolic responses of laying hens induced by high temperature at later laying stage, nine 60-wk-old laying hens (Gallus gallus domesticus) were employed in the present study. The hens were exposed to 32 degrees C for 21 d and blood samples were obtained before and at 1, 7, 14 and 21 d of heat exposure. The reactive oxygen species (ROS) formed in blood during heat exposure were estimated by the ex vivo spin-trapping method. Body temperature and plasma concentrations of glucose, urate, creatine kinase (CK), triiodothyronine (T(3)), thyroxine (T(4)), corticosterone (CORT), thiobarbituric acid reacting substances (TBARS), ferric/reducing antioxidant power (FRAP) and superoxide dismutase (SOD) activity were measured. Plasma levels of glucose, CK and CORT were not significantly influenced by heat exposure at any time point. The circulating concentrations of T(3) were decreased while plasma T(4) levels changed in the opposite way. The formation of ROS was significantly augmented by heat exposure in laying hens though the body temperature was not significantly altered. The enhanced enzymatic and non-enzymatic antioxidant systems acted in concert to alleviate the heat stress evoked oxidative damage.

Measuring oxygenation in vivo with MRS/MRI--from gas exchange to the cell

Oxygen plays a major role as a substrate in metabolic processes in numerous signaling pathways, in redox metabolism, and in free radical metabolism. To study the role of oxygen in normal and pathophysiological states, methods that can be used noninvasively are required. This review examines the potential of nuclear magnetic resonance techniques to study tissue oxygenation. It is written from a systems perspective, looking at detection methods with respect to the path that oxygen takes in the mammalian system-from the lungs, through the vascular system, into the interstitial space, and finally into the cell. Methods discussed range from those that are quantifiable, such as the assessment of spin lattice relaxation time in fluorocarbon solutions, to those that are more correlative, such as assessment of lactate and high energy phosphates. Since the methods vary in their site of application, sensitivity, and specificity to the quantification of oxygen, this review provides examples of how each method has been applied. This may facilitate the reader's understanding of how to optimally apply different methods to study specific biomedical problems.