Immuno-spin trapping analyses of DNA radicals

Detection and structural analysis of lipid-derived radicals in vitro and in vivo

Lipids can be oxidized by reactive oxygen species, resulting in lipid peroxidation and the formation of reactive metabolites such as lipid-derived electrophiles. These products have been reported to induce inflammation, angiogenesis, and ferroptosis. Lipid peroxidation can produce many different products, each of which performs a different function, and which can be challenging to detect in vivo. The initial products of lipid oxidation are lipid-derived radicals, which can cause extensive chain reactions leading to lipid peroxidation. Hence, the ability to detect lipid radicals may provide information about this important class of molecules and the mechanism by which they cause cellular and tissue damage in a wide range of oxidative conditions. In this review, we report recent scientific advances in the detection of lipid-derived radicals in vitro and in cultured cells. We also introduce the possibility of visualization and structural analysis of lipid-derived radicals generated not only in in cells but also in animal tissue samples from oxidative disease models, using fluorescence-based lipid radicals' detection probes. We anticipate that the various innovative techniques summarized in this paper will be applied and further developed to clarify the role of lipid peroxidation in the pathogenesis of oxidative stress-associated diseases.

Extracellular-vesicles delivered tumor-specific sequential nanocatalysts can be used for MRI-informed nanocatalytic Therapy of hepatocellular carcinoma

Background: Conventional therapeutic strategies for advanced hepatocellular carcinoma (HCC) remains a great challenge, therefore the alternative therapeutic modality for specific and efficient HCC suppression is urgently needed. Methods: In this work, HCC-derived extracellular vesicles (EVs) were applied as surface nanocarrier for sequential nanocatalysts GOD-ESIONs@EVs (GE@EVs) of tumor-specific and cascade nanocatalytic therapy against HCC. By enhancing the intracellular endocytosis through arginine-glycine-aspartic acid (RGD)-targeting effect and membrane fusion, sequential nanocatalysts led to more efficient treatment in the HCC tumor region in a shorter period of time. Results: Through glucose consumption as catalyzed by the loaded glucose oxidase (GOD) to overproduce hydrogen peroxide (H₂O₂), highly toxic hydroxyl radicals were generated by Fenton-like reaction as catalyzed by ESIONs, which was achieved under the mildly acidic tumor microenvironment, enabling the stimuli of the apoptosis and necrosis of HCC cells. This strategy demonstrated the high active-targeting capability of GE@EVs into HCC, achieving highly efficient tumor suppression both in vitro and in vivo. In addition, the as-synthesized nanoreactor could act as a desirable nanoscale contrast agent for magnetic resonance imaging, which exhibited desirable imaging capability during the sequential nanocatalytic treatment. Conclusion: This application of surface-engineering EVs not only proves the high-performance catalytic therapeutic modality of GE@EVs for HCC, but also broadens the versatile bio-applications of EVs.

Immuno-spin trapping of macromolecules free radicals in vitro and in vivo - One stop shopping for free radical detection

The only general technique that allows the unambiguous detection of free radicals is electron spin resonance (ESR). However, ESR spin trapping has severe limitations especially in biological systems. The greatest limitation of ESR is poor sensitivity relative to the low steady-state concentration of free radical adducts, which in cells and in vivo is much lower than the best sensitivity of ESR. Limitations of ESR have led to an almost desperate search for alternatives to investigate free radicals in biological systems. Here we explore the use of the immuno-spin trapping technique, which combine the specificity of the spin trapping to the high sensitivity and universal use of immunological techniques. All of the immunological techniques based on antibody binding have become available for free radical detection in a wide variety of biological systems.

Organic radical imaging in plants: Focus on protein radicals

Biomolecule (lipid and protein) oxidation products formed in plant cells exposed to photooxidative stress play a crucial role in the retrograde signaling and oxidative damage. The oxidation of biomolecules initiated by reactive oxygen species is associated with formation of organic (alkyl, peroxyl and alkoxyl) radicals. Currently, there is no selective and sensitive technique available for the detection of organic radicals in plant cells. Here, based on the analogy with animal cells, immuno-spin trapping using spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used to image organic radicals in Arabidopsis leaves exposed to high light. Using antibody raised against the DMPO nitrone adduct conjugated with the fluorescein isothiocyanate, organic radicals were imaged by confocal laser scanning microscopy. Organic radicals are formed predominantly in the chloroplasts located at the periphery of the cells and distributed uniformly throughout the grana stack. Characterization of protein radicals by standard immunological techniques using anti-DMPO antibody shows protein bands with apparent molecular weights of 32 and 34 kDa assigned to D1 and D2 proteins and two protein bands below the D1/D2 band with apparent molecular weights of 23 and 18 kDa and four protein bands above the D1/D2 band with apparent molecular weights of 41, 43, 55 and 68 kDa. In summary, imaging of organic radicals by immuno-spin trapping represents selective and sensitive technique for the detection of organic radicals that might help to clarify mechanistic aspects on the role of organic radicals in the retrograde signaling and oxidative damage in plant cell.

Immuno-Spin Trapping-Based Detection of Oxidative Modifications in Cardiomyocytes and Coronary Endothelium in the Progression of Heart Failure in Tgαq*44 Mice

Recent studies suggest both beneficial and detrimental role of increased reactive oxygen species and oxidative stress in heart failure (HF). However, it is not clear at which stage oxidative stress and oxidative modifications occur in the endothelium in relation to cardiomyocytes in non-ischemic HF. Furthermore, most methods used to date to study oxidative stress are either non-specific or require tissue homogenization. In this study, we used immuno-spin trapping (IST) technique with fluorescent microscopy-based detection of DMPO nitrone adducts to localize and quantify oxidative modifications of the hearts from Tgαq*44 mice; a murine model of HF driven by cardiomyocyte-specific overexpression of Gαq* protein. Tgαq*44 mice and age-matched FVB controls at early, transition, and late stages of HF progression were injected with DMPO in vivo and analyzed ex vivo for DMPO nitrone adducts signals. Progressive oxidative modifications in cardiomyocytes, as evidenced by the elevation of DMPO nitrone adducts, were detected in hearts from 10- to 16-month-old, but not in 8-month-old Tgαq*44 mice, as compared with age-matched FVB mice. The DMPO nitrone adducts were detected in left and right ventricle, septum, and papillary muscle. Surprisingly, significant elevation of DMPO nitrone adducts was also present in the coronary endothelium both in large arteries and in microcirculation simultaneously, as in cardiomyocytes, starting from 10-month-old Tgαq*44 mice. On the other hand, superoxide production in heart homogenates was elevated already in 6-month-old Tgαq*44 mice and progressively increased to high levels in 14-month-old Tgαq*44 mice, while the enzymatic activity of catalase, glutathione reductase, and glutathione peroxidase was all elevated as early as in 4-month-old Tgαq*44 mice and stayed at a similar level in 14-month-old Tgαq*44. In summary, this study demonstrates that IST represents a unique method that allows to quantify oxidative modifications in cardiomyocytes and coronary endothelium in the heart. In Tgαq*44 mice with slowly developing HF, driven by cardiomyocyte-specific overexpression of Gαq* protein, an increase in superoxide production, despite compensatory activation of antioxidative mechanisms, results in the development of oxidative modifications not only in cardiomyocytes but also in coronary endothelium, at the transition phase of HF, before the end-stage disease.

Detection of the formyl radical by EPR spin-trapping and mass spectrometry

For the first time we here present the unambiguous identification of the formyl radical (^•CHO) by EPR (Electron Paramagnetic Resonance) spectroscopy and mass spectrometry (MS) using DMPO (5,5-dimethyl-1-pyrroline N-oxide) as spin trap at ambient temperature without using any catalyst(s). The ^•CHO was continuously generated by UV photolysis in closed anoxic environment from pure formaldehyde (HCHO) in aqueous solution. The isotropic hyperfine structure constants of ^•CHO were determined as a_N = 15.72G and a_H = 21.27G. The signals were deconvoluted and split by simulation in their single adduct components: DMPO-CHO, DMPO-H and DMPO-OH. We verified our results at first using MNP (2-methyl-2-nitroso-propane) as spin trap with known literature data and then mass spectrometry. Similarly the MNP adduct components MNP-CHO, MNP-H as well as its own adduct, the MNP-2-methyl-2-propyl (MNP-MP) were deconvoluted. Due to the low signal intensities, we had to accumulate single measurements for both spin traps. Using MS we got the exact mass of the reduced ^•CHO adduct independently confirming the result of EPR detection of formyl radical.

Use of a cocktail of spin traps for fingerprinting large range of free radicals in biological systems

It is well established that the formation of radical species centered on various atoms is involved in the mechanism leading to the development of several diseases or to the appearance of deleterious effects of toxic molecules. The detection of free radical is possible using Electron Paramagnetic Resonance (EPR) spectroscopy and the spin trapping technique. The classical EPR spin-trapping technique can be considered as a "hypothesis-driven" approach because it requires an a priori assumption regarding the nature of the free radical in order to select the most appropriate spin-trap. We here describe a "data-driven" approach using EPR and a cocktail of spin-traps. The rationale for using this cocktail was that it would cover a wide range of biologically relevant free radicals and have a large range of hydrophilicity and lipophilicity in order to trap free radicals produced in different cellular compartments. As a proof-of-concept, we validated the ability of the system to measure a large variety of free radicals (O-, N-, C-, or S- centered) in well characterized conditions, and we illustrated the ability of the technique to unambiguously detect free radical production in cells exposed to chemicals known to be radical-mediated toxic agents.

Imaging free radicals in organelles, cells, tissue, and in vivo with immuno-spin trapping

The accurate and sensitive detection of biological free radicals in a reliable manner is required to define the mechanistic roles of such species in biochemistry, medicine and toxicology. Most of the techniques currently available are either not appropriate to detect free radicals in cells and tissues due to sensitivity limitations (electron spin resonance, ESR) or subject to artifacts that make the validity of the results questionable (fluorescent probe-based analysis). The development of the immuno-spin trapping technique overcomes all these difficulties. This technique is based on the reaction of amino acid- and DNA base-derived radicals with the spin trap 5, 5-dimethyl-1-pyrroline N-oxide (DMPO) to form protein- and DNA-DMPO nitroxide radical adducts, respectively. These adducts have limited stability and decay to produce the very stable macromolecule-DMPO-nitrone product. This stable product can be detected by mass spectrometry, NMR or immunochemistry by the use of anti-DMPO nitrone antibodies. The formation of macromolecule-DMPO-nitrone adducts is based on the selective reaction of free radical addition to the spin trap and is thus not subject to artifacts frequently encountered with other methods for free radical detection. The selectivity of spin trapping for free radicals in biological systems has been proven by ESR. Immuno-spin trapping is proving to be a potent, sensitive (a million times higher sensitivity than ESR), and easy (not quantum mechanical) method to detect low levels of macromolecule-derived radicals produced in vitro and in vivo. Anti-DMPO antibodies have been used to determine the distribution of free radicals in cells and tissues and even in living animals. In summary, the invention of the immuno-spin trapping technique has had a major impact on the ability to accurately and sensitively detect biological free radicals and, subsequently, on our understanding of the role of free radicals in biochemistry, medicine and toxicology.

Exercise and Oxidative Damage in Nucleoid DNA Quantified Using Single Cell Gel Electrophoresis: Present and Future Application

High intensity exercise can enhance the production of reactive oxygen and nitrogen free radical species, which may cause a number of perturbations to cellular integrity, including deoxyribonucleic acid (DNA) modification. In the absence of adequate DNA repair, it is theoretically possible that several biological disorders may ensue, in addition to premature aging. This striking hypothesis and supposition can only be realized in the presence of sound methodology for the quantification of DNA damage and repair. The alkaline single-cell gel electrophoresis or "comet assay" is a simple and reliable method for measuring the components of DNA stability in eukaryotic cells. The assay is commonly used in research associated with genotoxicology and in human bio-monitoring studies concerned with gene-environment interactions; but is currently less appreciated and under-utilized in the domain of exercise science. No exercise related study for example, has incorporated the comet assay combined with fluorescent in situ hybridization methodology to detect and investigate whole genome, telomeric DNA, or gene region-specific DNA damage and repair in cells. Our laboratory and others have used the comet assay in conjunction with lesion-specific endonucleases to measure DNA strand breaks and oxidized bases to confirm that high intensity exercise can damage and destabilize DNA. Thus, the primary function of this review is to highlight recent advances and innovation with the comet assay, in order to enhance our future understanding of the complex interrelationship between exercise and DNA modification in eukaryotic cells. A brief synopsis of the current literature addressing DNA stability as a function of continuous aerobic exercise is also included.

Metallothionein blocks oxidative DNA damage induced by acute inorganic arsenic exposure

We studied how protein metallothionein (MT) impacts arsenic-induced oxidative DNA damage (ODD) using cells that poorly express MT (MT-I/II double knockout embryonic cells; called MT-null cells) and wild-type (WT) MT competent cells. Arsenic (as NaAsO2) was less cytolethal over 24h in WT cells (LC50=11.0±1.3μM; mean±SEM) than in MT-null cells (LC50=5.6±1.2μM). ODD was measured by the immuno-spin trapping method. Arsenic (1 or 5μM; 24h) induced much less ODD in WT cells (121% and 141% of control, respectively) than in MT-null cells (202% and 260%). In WT cells arsenic caused concentration-dependent increases in MT expression (transcript and protein), and in the metal-responsive transcription factor-1 (MTF-1), which is required to induce the MT gene. In contrast, basal MT levels were not detectable in MT-null cells and unaltered by arsenic exposure. Transfection of MT-I gene into the MT-null cells markedly reduced arsenic-induced ODD levels. The transport genes, Abcc1 and Abcc2 were increased by arsenic in WT cells but either showed no or very limited increases in MT-null cells. Arsenic caused increases in oxidant stress defense genes HO-1 and GSTα2 in both WT and MT-null cells, but to much higher levels in WT cells. WT cells appear more adept at activating metal transport systems and oxidant response genes, although the role of MT in these responses is unclear. Overall, MT protects against arsenic-induced ODD in MT competent cells by potential sequestration of scavenging oxidant radicals and/or arsenic.

Redox regulation of NF-κB p50 and M1 polarization in microglia

Redox-signaling is implicated in deleterious microglial activation underlying CNS disease, but how ROS program aberrant microglial function is unknown. Here, the oxidation of NF-κB p50 to a free radical intermediate is identified as a marker of dysfunctional M1 (pro-inflammatory) polarization in microglia. Microglia exposed to steady fluxes of H2 O2 showed altered NF-κB p50 protein-protein interactions, decreased NF-κB p50 DNA binding, and augmented late-stage TNFα expression, indicating that H2 O2 impairs NF-κB p50 function and prolongs amplified M1 activation. NF-κB p50(-/-) mice and cultures exhibited a disrupted M2 (alternative) response and impaired resolution of the M1 response. Persistent neuroinflammation continued 1 week after LPS (1 mg/kg, IP) administration in the NF-κB p50(-/-) mice. However, peripheral inflammation had already resolved in both strains of mice. Treatment with the spin-trap DMPO mildly reduced LPS-induced 22 h TNFα in the brain in NF-κB p50(+/+) mice. Interestingly, DMPO failed to reduce and strongly augmented brain TNFα production in NF-κB p50(-/-) mice, implicating a fundamental role for NF-κB p50 in the regulation of chronic neuroinflammation by free radicals. These data identify NF-κB p50 as a key redox-signaling mechanism regulating the M1/M2 balance in microglia, where loss of function leads to a CNS-specific vulnerability to chronic inflammation.

DNA cleavage and detection of DNA radicals formed from hydralazine and copper (II) by ESR and immuno-spin trapping

Metal ion-catalyzed oxidation of hydrazine and its derivatives leads to the formation of the hydrazyl radical and subsequently to oxy-radicals in the presence of molecular oxygen. Here, we have examined the role of Cu(2+)-catalyzed oxidation of hydralazine in the induction of DNA damage. Neither 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) nor dimethyl sulfoxide (DMSO) was effective in inhibiting hydralazine-Cu(2+)-induced DNA damage. Singlet oxygen did not appear to participate in this DNA cleavage. The one-electron oxidation of hydralazine also leads to the formation of DNA radicals as confirmed by immuno-spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide. Electron spin resonance (ESR) and spin-trapping studies further confirmed the formation of DNA radicals; predominantly, 2'-deoxyadenosine radical adducts were detected, while some radicals were also detected with other nucleosides. Our results suggest that free hydroxyl radicals may not be the main damaging species causing DNA cleavage and that possibly Cu-peroxide complexes, formed from Cu(+)-H2O2, are responsible for this hydralazine-Cu(2+)-induced DNA cleavage.

Methylarsonous acid causes oxidative DNA damage in cells independent of the ability to biomethylate inorganic arsenic

Inorganic arsenic (iAs) and its toxic methylated metabolite, methylarsonous acid (MMA(III)), both have carcinogenic potential. Prior study shows iAs-induced malignant transformation in both arsenic methylation-proficient (liver) and methylation-deficient (prostate) cells, but only methylation-proficient cells show oxidative DNA damage (ODD) during this transformation. To further define whether arsenic methylation is necessary for transformation or ODD induction, here we chronically exposed these same liver or prostate cell lines to MMA(III) (0.25-1.0 μM) and tested for acquired malignant phenotype. Various metrics of oncogenic transformation were periodically assessed along with ODD during chronic MMA(III) exposure. Methylation-deficient and methylation-proficient cells both acquired a cancer phenotype with MMA(III) exposure at about 20 weeks, based on increased matrix metalloproteinase secretion, colony formation, and invasion. In contrast, prior work showed iAs-induced transformation took longer in biomethylation-deficient cells (~30 weeks) than in biomethylation-proficient cells (~18 weeks). In the present study, MMA(III) caused similar peak ODD levels at similar concentrations and at similar exposure times (18-22 weeks) in both cell types. At the approximate peak of ODD production, both cell types showed similar alterations in arsenic and oxidative stress adaptation factors (i.e., ABCC1, ABCC2, GST-π, SOD-1). Thus, MMA(III) causes oncogenic transformation associated with ODD in methylation-deficient cells, indicating that further methylation is not required to induce ODD. Together, these results show that MMA(III) and iAs cause an acquired malignant phenotype in methylation-deficient cells, yet iAs does not induce ODD. This indicates iAs likely has both genotoxic and non-genotoxic mechanisms dictated by the target cell's ability to methylate arsenic.

Chronic cadmium exposure in vitro induces cancer cell characteristics in human lung cells

Cadmium is a known human lung carcinogen. Here, we attempt to develop an in vitro model of cadmium-induced human lung carcinogenesis by chronically exposing the peripheral lung epithelia cell line, HPL-1D, to a low level of cadmium. Cells were chronically exposed to 5 μM cadmium, a noncytotoxic level, and monitored for acquired cancer characteristics. By 20 weeks of continuous cadmium exposure, these chronic cadmium treated lung (CCT-LC) cells showed marked increases in secreted MMP-2 activity (3.5-fold), invasion (3.4-fold), and colony formation in soft agar (2-fold). CCT-LC cells were hyperproliferative, grew well in serum-free media, and overexpressed cyclin D1. The CCT-LC cells also showed decreased expression of the tumor suppressor genes p16 and SLC38A3 at the protein levels. Also consistent with an acquired cancer cell phenotype, CCT-LC cells showed increased expression of the oncoproteins K-RAS and N-RAS as well as the epithelial-to-mesenchymal transition marker protein Vimentin. Metallothionein (MT) expression is increased by cadmium, and is typically overexpressed in human lung cancers. The major MT isoforms, MT-1A and MT-2A were elevated in CCT-LC cells. Oxidant adaptive response genes HO-1 and HIF-1A were also activated in CCT-LC cells. Expression of the metal transport genes ZNT-1, ZNT-5, and ZIP-8 increased in CCT-LC cells culminating in reduced cadmium accumulation, suggesting adaptation to the metal. Overall, these data suggest that exposure of human lung epithelial cells to cadmium causes acquisition of cancer cell characteristics. Furthermore, transformation occurs despite the cell's ability to adapt to chronic cadmium exposure.

Immuno-spin trapping from biochemistry to medicine: advances, challenges, and pitfalls. Focus on protein-centered radicals

BACKGROUND

Immuno-spin trapping (IST) is based on the reaction of a spin trap with a free radical to form a stable nitrone adduct, followed by the use of antibodies, rather than traditional electron paramagnetic resonance spectroscopy, to detect the nitrone adduct. IST has been successfully applied to mechanistic in vitro studies, and recently, macromolecule-centered radicals have been detected in models of drug-induced agranulocytosis, hepatotoxicity, cardiotoxicity, and ischemia/reperfusion, as well as in models of neurological, metabolic and immunological diseases.

SCOPE OF THE REVIEW

To critically evaluate advances, challenges, and pitfalls as well as the scientific opportunities of IST as applied to the study of protein-centered free radicals generated in stressed organelles, cells, tissues and animal models of disease and exposure.

MAJOR CONCLUSIONS

Because the spin trap has to be present at high enough concentrations in the microenvironment where the radical is formed, the possible effects of the spin trap on gene expression, metabolism and cell physiology have to be considered in the use of IST and in the interpretation of results. These factors have not yet been thoroughly dealt with in the literature.

GENERAL SIGNIFICANCE

The identification of radicalized proteins during cell/tissue response to stressors will help define their role in the complex cellular response to stressors and pathogenesis; however, the fidelity of spin trapping/immuno-detection and the effects of the spin trap on the biological system should be considered. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

Development of immunoblotting techniques for DNA radical detection

Radical damage to DNA has been implicated in cell death, cellular dysfunction, and cancer. A recently developed method for detecting DNA radicals uses the nitrone spin trap DMPO (5,5-dimethyl-1-pyrroline N-oxide) to trap radicals. The trapped radicals then decay into stable nitrone adducts detectable with anti-DMPO antibodies and quantifiable by ELISA or dot-blot assay. However, the sequences of DNA that are damaged are likely to be as important as the total level of damage. Therefore, we have developed immunoblotting methods for detection of DNA nitrone adducts on electrophoretically separated DNA, comparable to Western blotting for proteins. These new techniques not only allow the assessment of relative radical adduct levels, but can reveal specific DNA fragments, and ultimately nucleotides, as radical targets. Moreover, we have determined that denaturation of samples into single-stranded DNA enhances the detection of DNA-DMPO adducts in our new blotting methods and also in ELISA.

Oxidative DNA damage after acute exposure to arsenite and monomethylarsonous acid in biomethylation-deficient human cells

The carcinogen inorganic arsenic (iAs) undergoes biomethylation (BMT) in some cells. The methylated metabolite, monomethylarsonous (MMA(3+)), may cause oxidative DNA damage (ODD). With chronic iAs exposure, BMT-competent cells show ODD while BMT-deficient do not. To further define these events, we studied ODD produced by acute iAs or MMA(3+) in the BMT-deficient human prostate cell line, RWPE-1. ODD, measured by the immuno-spin trapping method, was assessed after exposure to iAs or MMA(3+) alone, with the arsenic BMT inhibitor selenite or after glutathione (GSH) depletion. The expression of oxidative stress-related genes (HO-1, SOD-1, SOD-2, Nrf2 and Keap-1) was also assessed. Exposure to iAs at 24 h (0-20 µM), stimulated ODD only at levels above the LC50 of a 48 h exposure (17 µM). If iAs induced ODD, it also activated oxidative stress-related genes. Selenium did not alter iAs-induced ODD. MMA(3+) at 24 h (0-0.5 µM) caused ODD at levels below the LC50 of a 48 h exposure (1.5 µM), which were greatly increased by GSH depletion but not selenite. MMA(3+) induced ODD at levels not activating oxidant stress response genes. Overall, iAs induced ODD in BMT-deficient cells only at toxic levels. MMA(3+) caused ODD at non-toxic levels, independently of cellular BMT capacity and in a fashion not requiring further BMT.

Metallothionein blocks oxidative DNA damage in vitro

The role of metallothionein (MT) in mitigation of oxidative DNA damage (ODD) induced by either cadmium (Cd) or the direct oxidant hydrogen peroxide (H(2)O(2)) was systematically examined using MT-I/II double knockout (MT-null) or MT-competent wild-type (WT) cells. Both toxicants were much more lethal to MT-null cells (Cd LC(50) = 6.6 μM; H(2)O(2) LC(50) = 550 μM) than to WT cells (Cd LC(50) = 16.5 μM; H(2)O(2) LC(50) = 930 μM). Cd induced concentration-related MT increases in WT cells, while the basal levels were undetectable and not increased by Cd in MT-null cells. ODD, measured by the immuno-spin trapping method, was minimally induced by sub-toxic Cd levels (1 or 5 μM; 24 h) in WT cells, but markedly increased in MT-null cells (>430 %). Similarly, ODD was induced to higher levels by lower concentrations of H(2)O(2) in MT-null cells than WT cells. Transfection of MT-I into MT-null cells reduced both Cd- and H(2)O(2)-induced cytolethality and ODD. Cd increased the expression of the oxidant defense genes, HO-1, and GSTa2 to a much greater extent in MT-null cells than in WT. Cd or H(2)O(2) exposure increased the expression of key transport genes, Mrp1 and Mrp2, in WT cells but not in MT-null cells. MT protects against Cd- and H(2)O(2)-induced ODD in MT-competent cells possibly by multiple mechanisms, potentially including direct metal ion sequestration and sequestration of oxidant radicals by MT. MT-deficient cells appear to adapt to Cd primarily by turning on oxidant response systems, while MT-competent cells activate MT and transport systems.

Measurement of intracellular biomolecular oxidation in liver ischemia-reperfusion injury via immuno-spin trapping

Hepatic ischemia-reperfusion (I/R) can lead to liver failure in association with remote organ damage, both of which have significant rates of morbidity and mortality. In this study, novel spin trapping and histopathological techniques have been used to investigate in vivo free radical formation in a rat model of warm liver I/R injury. 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) was administered to rats via intraperitoneal injection at a single dose of 1.5g of pure DMPO/kg body wt 2h before the initiation of liver ischemia. Blood vessels supplying the median and left lateral hepatic lobes were occluded with an arterial clamp for 60min, followed by 60min reperfusion. The effects of DMPO on I/R injury were evaluated by assessing the hepatic ultrastructure via transmission electron microscopy and by histopathological scoring. Immunoelectron microscopy was performed to determine the cellular localization of DMPO nitrone adducts. Levels of nitrone adducts were also measured to determine in situ scavenging of protein and DNA radicals. Total histopathological scoring of cellular damage was significantly decreased in hepatic I/R injury after DMPO treatment. DMPO treatment significantly decreased the hepatic conversion of xanthine oxidase and 4-hydroxynonenal formation in I/R injury compared to the untreated I/R group. The distribution of gold-nanoparticle-labeled DMPO nitrone adducts was observed in mitochondria, cytoplasm, and nucleus of hepatocytes. The formation of protein- and DNA-nitrone adducts was increased in DMPO-treated I/R livers compared to DMPO controls, indicating increased in situ protein and DNA radical formation and scavenging by DMPO. These results suggest that DMPO reduces I/R damage via protection against oxidative injury.

Detection and imaging of the free radical DNA in cells--site-specific radical formation induced by Fenton chemistry and its repair in cellular DNA as seen by electron spin resonance, immuno-spin trapping and confocal microscopy

Oxidative stress-related damage to the DNA macromolecule produces lesions that are implicated in various diseases. To understand damage to DNA, it is important to study the free radical reactions causing the damage. Measurement of DNA damage has been a matter of debate as most of the available methods measure the end product of a sequence of events and provide limited information on the initial free radical formation. We report a measurement of free radical damage in DNA induced by a Cu(II)-H₂O₂ oxidizing system using immuno-spin trapping supplemented with electron paramagnetic resonance. In this investigation, the short-lived radical generated is trapped by the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) immediately upon formation. The DMPO adduct formed is initially electron paramagnetic resonance active, but is subsequently oxidized to the stable nitrone adduct, which can be detected and visualized by immuno-spin trapping and has the potential to be further characterized by other analytical techniques. The radical was found to be located on the 2′-deoxyadenosine (dAdo) moiety of DNA. The nitrone adduct was repaired on a time scale consistent with DNA repair. In vivo experiments for the purpose of detecting DMPO–DNA nitrone adducts should be conducted over a range of time in order to avoid missing adducts due to the repair processes.

Arsenic transformation predisposes human skin keratinocytes to UV-induced DNA damage yet enhances their survival apparently by diminishing oxidant response

Inorganic arsenic and UV, both human skin carcinogens, may act together as skin co-carcinogens. We find human skin keratinocytes (HaCaT cells) are malignantly transformed by low-level arsenite (100nM, 30weeks; termed As-TM cells) and with transformation concurrently undergo full adaptation to arsenic toxicity involving reduced apoptosis and oxidative stress response to high arsenite concentrations. Oxidative DNA damage (ODD) is a possible mechanism in arsenic carcinogenesis and a hallmark of UV-induced skin cancer. In the current work, inorganic arsenite exposure (100nM) did not induce ODD during the 30weeks required for malignant transformation. Although acute UV-treatment (UVA, 25J/cm(2)) increased ODD in passage-matched control cells, once transformed by arsenic to As-TM cells, acute UV actually further increased ODD (>50%). Despite enhanced ODD, As-TM cells were resistant to UV-induced apoptosis. The response of apoptotic factors and oxidative stress genes was strongly mitigated in As-TM cells after UV exposure including increased Bcl2/Bax ratio and reduced Caspase-3, Nrf2, and Keap1 expression. Several Nrf2-related genes (HO-1, GCLs, SOD) showed diminished responses in As-TM cells after UV exposure consistent with reduced oxidant stress response. UV-exposed As-TM cells showed increased expression of cyclin D1 (proliferation gene) and decreased p16 (tumor suppressor). UV exposure enhanced the malignant phenotype of As-TM cells. Thus, the co-carcinogenicity between UV and arsenic in skin cancer might involve adaptation to chronic arsenic exposure generally mitigating the oxidative stress response, allowing apoptotic by-pass after UV and enhanced cell survival even in the face of increased UV-induced oxidative stress and increased ODD.

Site-specific radical formation in DNA induced by Cu(II)-H₂O₂ oxidizing system, using ESR, immuno-spin trapping, LC-MS, and MS/MS

Oxidative stress-related damage to the DNA macromolecule produces a multitude of lesions that are implicated in mutagenesis, carcinogenesis, reproductive cell death, and aging. Many of these lesions have been studied and characterized by various techniques. Of the techniques that are available, the comet assay, HPLC-EC, GC-MS, HPLC-MS, and especially HPLC-MS/MS remain the most widely used and have provided invaluable information on these lesions. However, accurate measurement of DNA damage has been a matter of debate. In particular, there have been reports of artifactual oxidation leading to erroneously high damage estimates. Further, most of these techniques measure the end product of a sequence of events and thus provide only limited information on the initial radical mechanism. We report here a qualitative measurement of DNA damage induced by a Cu(II)-H₂O₂ oxidizing system using immuno-spin trapping (IST) with electron paramagnetic resonance (EPR), MS, and MS/MS. The radical generated is trapped by DMPO immediately upon formation. The DMPO adduct formed is initially EPR active but subsequently is oxidized to the stable nitrone, which can then be detected by IST and further characterized by MS and MS/MS.

Oxidative stress induces protein and DNA radical formation in follicular dendritic cells of the germinal center and modulates its cell death patterns in late sepsis

Profound depletion of follicular dendritic cells (FDCs) is a hallmark of sepsis-like syndrome, but the exact causes of the ensuing cell death are unknown. The cell death-driven depletion contributes to immunoparalysis and is responsible for most of the morbidity and mortality in sepsis. Here we have utilized immuno-spin trapping, a method for detection of free radical formation, to detect oxidative stress-induced protein and DNA radical adducts in FDCs isolated from the spleens of septic mice and from human tonsil-derived HK cells, a subtype of germinal center FDCs, to study their role in FDC depletion. At 24h post-lipopolysaccharide administration, protein radical formation and oxidation were significantly elevated in vivo and in HK cells as shown by ELISA and confocal microscopy. The xanthine oxidase inhibitor allopurinol and the iron chelator desferrioxamine significantly decreased the formation of protein radicals, suggesting the role of xanthine oxidase and Fenton-like chemistry in radical formation. Protein and DNA radical formation correlated mostly with apoptotic features at 24h and necrotic morphology of all the cell types studied at 48h with concomitant inhibition of caspase-3. The cytotoxicity of FDCs resulted in decreased CD45R/CD138-positive plasma cell numbers, indicating a possible defect in B cell differentiation. In one such mechanism, radical formation initiated by xanthine oxidase formed protein and DNA radicals, which may lead to cell death of germinal center FDCs.

Oxidative stress studies of six TiO₂ and two CeO₂ nanomaterials: immuno-spin trapping results with DNA

Six TiO₂ and two CeO₂ nanomaterials with dry sizes ranging from 6-410 nm were tested for their ability to cause DNA centered free radicals in vitro in the concentration range of 10-3,000 ug/ml. All eight of the nanomaterials significantly increased the adduction of the spin trap agent 5,5-dimethyl-1-pyroline N-oxide (DMPO) to DNA as measured by the experimental technique of immuno-spin trapping. The eight nanomaterials differed considerably in their potency, slope, and active concentration. The largest increase in DNA nitrone adducts was caused by a TiO₂ nanomaterial (25 nm, anatase) from Alfa Aesar. Some nanomaterials that increased the amount of DNA nitrone adducts at the lowest exposure concentrations (100 ug/ml) were Degussa TiO₂ (31 nm), Alfa Aesar TiO₂ (25 nm, anatase) and Nanoamor CeO₂ (8 nm, cerianite). At exposure concentrations of 10 or 30 ug/ml, no nanomaterials showed significant in vitro formation of DNA nitrone adducts.

Oxidatively generated base damage to cellular DNA

Search for the formation of oxidatively base damage in cellular DNA has been a matter of debate for more than 40 years due to the lack of accurate methods for the measurement of the lesions. HPLC associated with either tandem mass spectrometry (MS/MS) or electrochemical detector (ECD) together with optimized DNA extraction conditions constitutes a relevant analytical approach. This has allowed the accurate measurement of oxidatively generated single and clustered base damage in cellular DNA following exposure to acute oxidative stress conditions mediated by ionizing radiation, UVA light and one-electron oxidants. In this review the formation of 11 single base lesions that is accounted for by reactions of singlet oxygen, hydroxyl radical or high intensity UVC laser pulses with nucleobases is discussed on the basis of the mechanisms available from model studies. In addition several clustered lesions were found to be generated in cellular DNA as the result of one initial radical hit on either a vicinal base or the 2-deoxyribose. Information on nucleobase modifications that are formed upon addition of reactive aldehydes arising from the breakdown of lipid hydroperoxides is also provided.

Myeloperoxidase-induced genomic DNA-centered radicals

Myeloperoxidase (MPO) released by activated neutrophils can initiate and promote carcinogenesis. MPO produces hypochlorous acid (HOCl) that oxidizes the genomic DNA in inflammatory cells as well as in surrounding epithelial cells. DNA-centered radicals are early intermediates formed during DNA oxidation. Once formed, DNA-centered radicals decay by mechanisms that are not completely understood, producing a number of oxidation products that are studied as markers of DNA oxidation. In this study we employed the 5,5-dimethyl-1-pyrroline N-oxide-based immuno-spin trapping technique to investigate the MPO-triggered formation of DNA-centered radicals in inflammatory and epithelial cells and to test whether resveratrol blocks HOCl-induced DNA-centered radical formation in these cells. We found that HOCl added exogenously or generated intracellularly by MPO that has been taken up by the cell or by MPO newly synthesized produces DNA-centered radicals inside cells. We also found that resveratrol passed across cell membranes and scavenged HOCl before it reacted with the genomic DNA, thus blocking DNA-centered radical formation. Taken together our results indicate that the formation of DNA-centered radicals by intracellular MPO may be a useful point of therapeutic intervention in inflammation-induced carcinogenesis.

Requirement of arsenic biomethylation for oxidative DNA damage

BACKGROUND

Inorganic arsenic is an environmental carcinogen that may act through multiple mechanisms including formation of methylated derivatives in vivo. Sodium arsenite (up to 5.0 microM) renders arsenic methylation-competent TRL1215 rat liver epithelial cells tumorigenic in nude mice at 18 weeks of exposure and arsenic methylation-deficient RWPE-1 human prostate epithelial cells tumorigenic at 30 weeks of exposure. We assessed the role of arsenic biomethylation in oxidative DNA damage (ODD) using a recently developed immuno-spin trapping method.

METHODS

Immuno-spin trapping was used to measure ODD after chronic exposure of cultured TRL1215 vs RWPE-1 cells, or of methylation-competent UROtsa/F35 vs methylation-deficient UROtsa human urothelial cells, to sodium arsenite. Secreted matrix metalloproteinase (MMP)-2 and -9 activity, as analyzed by zymography, cellular invasiveness by using a transwell assay, and colony formation by using soft agar assay were compared in cells exposed to arsenite with and without selenite, an arsenic biomethylation inhibitor, to assess the role of ODD in the transition to an in vitro cancer phenotype.

RESULTS

Exposure of methylation-competent TRL1215 cells to up to 1.0 microM sodium arsenite was followed by a substantial increase in ODD at 5-18 weeks (eg, at 16 weeks with 1.0 microM arsenite, 1138% of control, 95% confidence interval [CI] = 797% to 1481%), whereas exposure of methylation-deficient RWPE-1 cells to up to 5.0 microM arsenite did not increase ODD for a 30-week period. Inhibition of arsenic biomethylation with sodium selenite abolished arsenic-induced ODD and invasiveness, colony formation, and MMP-2 and -9 hypersecretion in TRL1215 cells. Arsenic induced ODD in methylation-competent UROtsa/F35 cells (eg, at 16 weeks, with 1.0 microM arsenite 225% of control, 95% CI = 188% to 262%) but not in arsenic methylation-deficient UROtsa cells, and ODD levels corresponded to the levels of increased invasiveness, colony formation, and hypersecretion of active MMP-2 and -9 seen after transformation to an in vitro cancer phenotype.

CONCLUSION

Arsenic biomethylation appears to be obligatory for arsenic-induced ODD and appears linked in some cells with the accelerated transition to an in vitro cancer phenotype.

Single gold nanoparticles counter: an ultrasensitive detection platform for one-step homogeneous immunoassays and DNA hybridization assays

In this paper, we present for the first time a single gold nanoparticle counter (SGNPC) in solution based on the photon bursting in a highly focused laser beam (less than 1 fL) due to the plasmon resonance scattering and Brownian motion of gold nanoparticles (GNPs). The photon burst intensity of single 36 nm GNPs is several tens to hundreds times stronger than that of quantum dots (QDs) and organic dyes. The relationship between the photon burst counts and GNPs concentration shows an excellent linearity. The linear range is over 4 orders of magnitude, and the detection limit of GNPs (36 nm) is 17 fM. On the basis of this single nanoparticle technique, we developed an ultrasensitive and highly selective detection platform for homogeneous immunoassay and DNA hybridization assays using GNPs as probes, which were 2-5 orders of magnitude more sensitive than current homogeneous methods. We used this technology to construct homogeneous sandwich immunoassays for cancer biomarkers, such as carcinoembryonic antigen (CEA) and alpha fetal protein (AFP), and aptamer recognition for thrombin. The detection limits are 130 fM for CEA, 714 fM for AFP and 2.72 pM for thrombin. Our method was successfully applied for direct determination of CEA, AFP and thrombin levels in sera from healthy subjects and cancer patients. In homogeneous DNA hybridization detection, we chose methylenetetrahydrofolate reductase (MTHFR) gene as a target. This assay successfully distinguished DNA sequences with single base mismatches, and the detection limits for the target were at 1 fM level.

Immuno-spin trapping of protein and DNA radicals: "tagging" free radicals to locate and understand the redox process

Biomolecule-centered radicals are intermediate species produced during both reversible (redox modulation) and irreversible (oxidative stress) oxidative modification of biomolecules. These oxidative processes must be studied in situ and in real time to understand the molecular mechanism of cell adaptation or death in response to changes in the extracellular environment. In this regard, we have developed and validated immuno-spin trapping to tag the redox process, tracing the oxidatively generated modification of biomolecules, in situ and in real time, by detecting protein- and DNA-centered radicals. The purpose of this methods article is to introduce and update the basic methods and applications of immuno-spin trapping for the study of redox biochemistry in oxidative stress and redox regulation. We describe in detail the production, detection, and location of protein and DNA radicals in biochemical systems, cells, and tissues, and in the whole animal as well, by using immuno-spin trapping with the nitrone spin trap 5,5-dimethyl-1-pyrroline N-oxide.

Cu,Zn-superoxide dismutase-driven free radical modifications: copper- and carbonate radical anion-initiated protein radical chemistry

The understanding of the mechanism, oxidant(s) involved and how and what protein radicals are produced during the reaction of wild-type SOD1 (Cu,Zn-superoxide dismutase) with H2O2 and their fate is incomplete, but a better understanding of the role of this reaction is needed. We have used immuno-spin trapping and MS analysis to study the protein oxidations driven by human (h) and bovine (b) SOD1 when reacting with H2O2 using HSA (human serum albumin) and mBH (mouse brain homogenate) as target models. In order to gain mechanistic information about this reaction, we considered both copper- and CO3(*-) (carbonate radical anion)-initiated protein oxidation. We chose experimental conditions that clearly separated SOD1-driven oxidation via CO(*-) from that initiated by copper released from the SOD1 active site. In the absence of (bi)carbonate, site-specific radical-mediated fragmentation is produced by SOD1 active-site copper. In the presence of (bi)carbonate and DTPA (diethylenetriaminepenta-acetic acid) (to suppress copper chemistry), CO(*-) produced distinct radical sites in both SOD1 and HSA, which caused protein aggregation without causing protein fragmentation. The CO(*-) produced by the reaction of hSOD1 with H2O2 also produced distinctive DMPO (5,5-dimethylpyrroline-N-oxide) nitrone adduct-positive protein bands in the mBH. Finally, we propose a biochemical mechanism to explain CO(*-) production from CO2, enhanced protein radical formation and protection by (bi)carbonate against H2O2-induced fragmentation of the SOD1 active site. Our present study is important for establishing experimental conditions for studying the molecular mechanism and targets of oxidation during the reverse reaction of SOD1 with H2O2; these results are the first step in analysing the critical targets of SOD1-driven oxidation during pathological processes such as neuroinflammation.

Superoxide dismutase 1-mediated production of ethanol- and DNA-derived radicals in yeasts challenged with hydrogen peroxide: molecular insights into the genome instability of peroxiredoxin-null strains

Peroxiredoxins are receiving increasing attention as defenders against oxidative damage and sensors of hydrogen peroxide-mediated signaling events. In the yeast Saccharomyces cerevisiae, deletion of one or more isoforms of the peroxiredoxins is not lethal but compromises genome stability by mechanisms that remain under scrutiny. Here, we show that cytosolic peroxiredoxin-null cells (tsa1Deltatsa2Delta) are more resistant to hydrogen peroxide than wild-type (WT) cells and consume it faster under fermentative conditions. Also, tsa1Deltatsa2Delta cells produced higher yields of the 1-hydroxyethyl radical from oxidation of the glucose metabolite ethanol, as proved by spin-trapping experiments. A major role for Fenton chemistry in radical formation was excluded by comparing WT and tsa1Deltatsa2Delta cells with respect to their levels of total and chelatable metal ions and of radical produced in the presence of chelators. The main route for 1-hydroxyethyl radical formation was ascribed to the peroxidase activity of Cu,Zn-superoxide dismutase (Sod1), whose expression and activity increased approximately 5- and 2-fold, respectively, in tsa1Deltatsa2Delta compared with WT cells. Accordingly, overexpression of human Sod1 in WT yeasts led to increased 1-hydroxyethyl radical production. Relevantly, tsa1Deltatsa2Delta cells challenged with hydrogen peroxide contained higher levels of DNA-derived radicals and adducts as monitored by immuno-spin trapping and incorporation of (14)C from glucose into DNA, respectively. The results indicate that part of hydrogen peroxide consumption by tsa1Deltatsa2Delta cells is mediated by induced Sod1, which oxidizes ethanol to the 1-hydroxyethyl radical, which, in turn, leads to increased DNA damage. Overall, our studies provide a pathway to account for the hypermutability of peroxiredoxin-null strains.