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It is widely accepted that free radicals in tobacco smoke lead to oxidative stress and generate the popular lipid peroxidation biomarker 8-iso-prostaglandin F2α (8-iso-PGF2α). However, 8-iso-PGF2α can simultaneously be produced in vivo by the prostaglandin-endoperoxide synthases (PGHS) induced by inflammation. This inflammation-dependent mechanism has never been considered as a source of elevated 8-iso-PGF2α in tobacco smokers. The goal of this study is to quantify the distribution of chemical- and PGHS-dependent 8-iso-PGF2α formation in the plasma of tobacco smokers and non-smokers. The influences of gender and hormonal contraceptive use were accounted for. The distribution was determined by measuring the 8-iso-PGF2α/prostaglandin F2α (PGF2α) ratio. When comparing smokers (n = 28) against non-smokers (n = 30), there was a statistically significant increase in the 8-iso-PGF2α concentration. The source of this increased 8-iso-PGF2α was primarily from PGHS. When stratifying for gender, the increase in 8-iso-PGF2α in male smokers (n = 9) was primarily from PGHS. Interestingly, female smokers on hormonal contraceptives had increased 8-iso-PGF2α in both pathways, whereas those not on hormonal contraceptives did not have increased 8-iso-PGF2α. In conclusion, increased plasma 8-iso-PGF2α in tobacco smokers has complex origins, with PGHS-dependent formation as the primary source. Accounting for both pathways provides a definitive measurement of both oxidative stress and inflammation.

The acute ozone induced lung injury model has been widely used to explore injury and repair processes induced by oxidant overload. The current study evaluated acute ozone exposure effects on prostaglandin F2α (PGF2α) in male Fischer rat plasma and urine with the hypothesis that ozone may induce an inflammatory response in the body that can be measured by the induction of PGF2α. That might then lead to the identification of potential marker for acute lung injury through systemic inflammation. The time and dose-dependent effects of ozone exposure on the plasma and urinary levels of a major PGF2α metabolite15-keto-dihydro-PGF2α were determined using a radioimmunoassay. No statistically significant differences in the PGF2α metabolite were found between the control and the experimental groups at either ozone exposure dose (2ppm and 5ppm) or any time point (2h, 7h and 16h) post exposure for plasma and at 7 different post exposure time points (between 2 and 80h) for urine. It is concluded that acute ozone exposure does not cause changes in plasma and urinary PGF2α, and therefore their measurement in plasma and urine may not be used to reveal pulmonary inflammation and damage by ozone.

Exposure to phthalates has been linked to many adverse birth outcomes including preterm birth and preeclampsia. One mechanism behind these associations may be oxidative stress, which is best estima...

The notion that oxidative stress plays a role in virtually every human disease and environmental exposure has become ingrained in everyday knowledge. However, mounting evidence regarding the lack of specificity of biomarkers traditionally used as indicators of oxidative stress in human disease and exposures now necessitates re-evaluation. To prioritize these re-evaluations, published literature was comprehensively analyzed in a meta-analysis to quantitatively classify the levels of systemic oxidative damage across human disease and in response to environmental exposures. In this meta-analysis, the F2-isoprostane, 8-iso-PGF2α, was specifically chosen as the representative marker of oxidative damage. To combine published values across measurement methods and specimens, the standardized mean differences (Hedges’ g) in 8-iso-PGF2α levels between affected and control populations were calculated. The meta-analysis resulted in a classification of oxidative damage levels as measured by 8-iso-PGF2α across 50 human health outcomes and exposures from 242 distinct publications. Relatively small increases in 8-iso-PGF2α levels (g, Graphical abstract fx1, Highlights • Oxidative damage is highly variable in human conditions as measured by F2-isoprostanes. • Respiratory tract and urogenital diseases have the highest F2-isoprostanes. • Cancer and cardiovascular diseases have surprisingly low F2-isoprostanes.

F2-isoprostanes, 8-iso-PGF2α, have been quantified as biomarkers of oxidative stress in over 1000 distinct experimental and human conditions. However, it has been shown that in addition to the free radical mediated pathway, the inflammation-induced prostaglandin-H-synthase enzymes are a major source of the F2-isoprostane generation. Accounting for the inflammatory source, F2-isoprostanes can be utilized for either a specific biomarker of oxidative stress or a biomarker of inflammation. To distinguish between F2-isoprostanes generated from inflammation vs. oxidative stress, the 8-iso-PGF2α/PGF2α ratio was implemented. With this measure, we have verified that exposure to the classic free radical toxicant carbon tetrachloride in rats predominantly causes an increase in chemical 8-iso-PGF2α (86.6 ± 8.0 % of total at 1200 mg/kg). In contrast, exposure to lipopolysaccharide also induces the formation of F2-isoprostanes; however, the predominant mechanism for this exposure is due to increased enzymatic 8-iso-PGF2α (59.5 ± 7.0 % of total at 0.5 mg/kg). Surprisingly, in human tobacco smokers, we also found that enzymatic lipid peroxidation is the primary source of F2-isoprostanes (Hedges’ g = 0.59 for enzymatic vs. 0.35 for chemical 8-iso-PGF2α). This distribution was independent of sex and age. Another source associated with elevated levels of 8-iso-PGF2α in humans is increased urinary phthalate metabolites and most research has concluded oxidative stress mediated phthalate exposure. In a large population of pregnant women, (N ~ 700), we observed compound dependent associations with lower molecular weight phthalate metabolites being associated with higher levels of chemical 8-iso-PGF2α whereas specific higher, branched chain metabolites are associated with elevated levels of enzymatic 8-iso-PGF2α. Our experimental and human data show the exposure dependent changes in 8-iso-PGF2α and the importance of distinguishing its sources to make it a specific biomarker of oxidative stress or inflammation. Without this additional step of 8-iso-PGF2α / PGF2α ratio determination, data can be greatly misinterpreted.

Today's developed world faces a major public health challenge in the rise in the obese population and the increased incidence in fatty liver disease. There is a strong association among diet induced obesity, fatty liver disease and development of nonalcoholic steatohepatitis but the environmental link to disease progression remains unclear. Here we demonstrate that in obesity, early steatohepatitic lesions induced by the water disinfection byproduct bromodichloromethane are mediated by increased oxidative stress and leptin which act in synchrony to potentiate disease progression. Low acute exposure to bromodichloromethane (BDCM), in diet-induced obesity produced oxidative stress as shown by increased lipid peroxidation, protein free radical and nitrotyrosine formation and elevated leptin levels. Exposed obese mice showed histopathological signs of early steatohepatitic injury and necrosis. Spontaneous knockout mice for leptin or systemic leptin receptor knockout mice had significantly decreased oxidative stress and TNF-α levels. Co-incubation of leptin and BDCM caused Kupffer cell activation as shown by increased MCP-1 release and NADPH oxidase membrane assembly, a phenomenon that was decreased in Kupffer cells isolated from leptin receptor knockout mice. In obese mice that were BDCM-exposed, livers showed a significant increase in Kupffer cell activation marker CD68 and, increased necrosis as assessed by levels of isocitrate dehydrogenase, events that were decreased in the absence of leptin or its receptor. In conclusion, our results show that exposure to the disinfection byproduct BDCM in diet-induced obesity augments steatohepatitic injury by potentiating the effects of leptin on oxidative stress, Kupffer cell activation and cell death in the liver.

Although it is widely known that arsenic-contaminated drinking water causes many diseases, arsenic's exact mode of action (MOA) is not fully understood. Induction of oxidative stress has been proposed as an important key event in the toxic MOA of arsenic. The authors' studies are centered on identifying a reactive species involved in the genotoxicity of arsenic using a catalase (CAT) knockout mouse model that is impaired in its ability to breakdown hydrogen peroxide (H2O2). The authors assessed the induction of DNA damage using the Comet assay following exposure of mouse Cat+/+ and Cat−/− primary splenic lymphocytes to monomethylarsonous acid (MMAIII) to identify the potential role of H2O2 in mediating cellular effects of this metalloid. The results showed that the Cat−/− lymphocytes are more susceptible to MMAIII than the Cat+/+ lymphocytes by a small (1.5-fold) but statistically significant difference. CAT activity assays demonstrated that liver tissue has approximately three times more CAT activity than lymphocytes. Therefore, Comet assays were performed on primary Cat+/+, Cat+/−, and Cat−/− hepatocytes to determine if the Cat−/− cells were more susceptible to MMAIII than lymphocytes. The results showed that the Cat−/− hepatocytes exhibit higher levels of DNA strand breakage than the Cat+/+ (approximately fivefold) and Cat+/− (approximately twofold) hepatocytes exposed to MMAIII. Electron spin resonance using 5,5-dimethyl-1-pyrroline-N-oxide as the spin-trap agent detected the generation of ·OH via MMAIII when H2O2 was present. These experiments suggest that CAT is involved in protecting cells against the genotoxic effects of the ·OH generated by MMAIII. Environ. Mol. Mutagen. 54:317–326, 2013. © 2013 Wiley Periodicals, Inc.

Cumene hydroperoxide (CHP) is a high production volume chemical that is used to generate phenol and acetone. Dermal exposure to CHP was hypothesized to result in systemic tissue toxicity, production of free radicals, and consequent decrease in plasma antioxidant levels. To evaluate the hypothesis and characterize the toxicity of CHP, male and female B6C3F1/N mice and F344/N rats were exposed to varying doses of CHP applied topically for 14 or 90 days. No significant changes in survival or body weight of mice and rats were observed following 14 days of exposure. However, 90 days of CHP exposure at the high dose (12 mg/kg) triggered a significant decrease (−15%) in the body weight of the male rat group only. Irritation of the skin was observed at the site of application and was characterized by inflammation and epidermal hyperplasia. In treated animals, histology of liver tissue, free radical generation, and antioxidant levels in blood plasma were not significantly changed as compared to the corresponding controls. Consistent with the lack of systemic damage, no increase in micronucleated erythrocytes was seen in peripheral blood. In conclusion, topical CHP application caused skin damage only at the application site and did not cause systemic tissue impairment.

Oxidative stress is elevated in numerous environmental exposures and diseases. Millions of dollars have been spent to try to ameliorate this damaging process using anti-oxidant therapies. Currently, the best accepted biomarker of oxidative stress is the lipid oxidation product 8-isoprostaglandin F(2α) (8-iso-PGF(2α)), which has been measured in over a thousand human and animal studies. 8-iso-PGF(2α) generation has been exclusively attributed to nonenzymatic chemical lipid peroxidation (CLP). However, 8-iso-PGF(2α) can also be produced enzymatically by the prostaglandin-endoperoxide synthases (PGHS) in vivo. When failing to account for PGHS-dependent generation, 8-iso-PGF(2α) cannot be interpreted as a selective biomarker of oxidative stress. We investigated the formation of 8-iso-PGF(2α) in rats exposed to carbon tetrachloride (CCl(4)) or lipopolysaccharide (LPS) using the 8-iso-PGF(2α)/PGF(2α) ratio to quantitatively determine the source(s) of 8-iso-PGF(2α). Upon exposure to a 120 mg/kg dose of CCl(4), the contribution of CLP accounted for only 55.6 ± 19.4% of measured 8-iso-PGF(2α), whereas in the 1200 mg/kg dose, CLP was the predominant source of 8-iso-PGF(2α) (86.6 ± 8.0% of total). In contrast to CCl(4), exposure to 0.5 mg/kg LPS was characterized by a significant increase in both the contribution of PGHS (59.5 ± 7.0) and CLP (40.5 ± 14.0%). In conclusion, significant generation of 8-iso-PGF(2α) occurs through enzymatic as well as chemical lipid peroxidation. The distribution of the contribution is dependent on the exposure agent as well as the dose. The 8-iso-PGF(2α)/PGF(2α) ratio accurately determines the source of 8-iso-PGF(2α) and provides an absolute measure of oxidative stress in vivo.

Tert-butyl hydroperoxide (TBHP) is a catalyst frequently used in oxidation and sulfonation reactions in the plastics industry. Since the toxicological evaluation of TBHP remains unknown, the National Toxicology Program (NTP) designed studies to characterize and compare TBHP toxicity by the dermal and oral (gavage) routes in male and female Fischer 344 rats and B6C3F1 mice in 14-day exposures. Rats and mice were administered TBHP at 22, 44, 88, 176 or 352 mg/kg in 0.5% aqueous methylcellulose for the gavage studies. In the dermal studies, mice were administered the same doses as above, while rats were administered four doses (22, 44, 88, 176 mg/kg) in 50% aqueous acetone. Results from the gavage studies revealed treatment-related decreases in survival in male rats and body weights in both male and female rats in the 352 mg/kg group. Clinical signs included post-treatment lethargy, thinness, abnormal breathing, ruffled fur, and/or ataxia which occurred sporadically. The male mice showed a statistically significant decrease in body weight in the 44, 88, 176, and 352 mg/kg groups. The major target organs of toxicity were the forestomach in male and female rats and mice, and the esophagus in male and female rats and in male mice. In addition, there was an increase in the absolute and relative liver weight in female mice with hepatocellular hypertrophy in the top-dose group only. Results from spin trapping experiments revealed the presence of electron paramagnetic resonance signals from radical adducts in the blood and organic extracts of the liver and kidneys of rats treated by gavage with 176 mg/kg TBHP, suggesting the involvement of free- radical generation. The no observed adverse effect level (NOAEL) was considered to be 22 mg/kg in rats and male mice, and 44 mg/kg in female mice. In the dermal studies, there was no effect on survival, body weight, or organ weights in either rats or mice. TBHP administration at the site of application resulted in dermal irritation, hyperkeratosis, hyperplasia, and/or inflammation of the epidermis and inflammation of the dermis at 176 mg/kg and above in male and female rats. Dermal irritation at the site of application was noted in all the mice exposed to 352 mg/kg TBHP. Histopathological lesions in the epidermis and dermis were seen in the 88-352 mg/kg males and in the 176-352 mg/kg females. The NOAEL was found to be 88 mg/kg for male rats and female mice, and 44 mg/kg for female rats and male mice. In conclusion, these studies demonstrate that TBHP is metabolized to free radicals and is a contact irritant affecting skin by the dermal route of exposure, and forestomach and esophagus by oral administration. There was no evidence of systemic absorption by the dermal route of exposure based on lack of pathological findings (Supported by National Institute of Environmental Health Sciences Contract No. N01-ES-65406).

The prevailing viewpoint from decades of research on biomarkers of oxidative stress such as the F2-isoprostanes has been that increased oxidative damage plays an important role in the etiology of many human conditions. However, due to a lack of mechanistic verification of the F2-isoprostane source combined with a sole focus on detecting statistically significant changes, the specificity and utility of these results may have been misinterpreted. F2-isoprostanes have been quantified as biomarkers of oxidative stress in over 50 distinct human conditions ranging from Alzheimer’s to tobacco smoking (223 references). Despite its popularity, the specificity of F2-isoprostanes as biomarkers of oxidative stress is in question. It has been shown that the inflammation-induced prostaglandin-H-synthase enzymes are a major source of the F2-isoprostane, 8-iso-PGF2α. Without accounting for the inflammatory source, F2-isoprostanes cannot be utilized as a specific biomarker of oxidative stress. To distinguish between F2-isoprostanes generated from inflammation vs. oxidative stress, the 8-iso-PGF2α/PGF2α was invented. With this measure, we have verified that exposure to the classic free radical toxicant carbon tetrachloride in rats predominantly causes an increase in chemical lipid peroxidation (86.6 ± 8.0 % of total at 1200 mg/kg). In contrast, exposure to lipopolysaccharide also induces the formation of F2-isoprostanes, however, the predominant mechanism for this exposure is due to increased enzymatic lipid peroxidation (59.5 ± 7.0 % of total at 0.5 mg/kg). Surprisingly, in human tobacco smokers, we also found that enzymatic lipid peroxidation is the primary source of F2-isoprostanes (Hedges’ g = 0.59 for enzymatic vs. 0.35 for chemical). This distribution was independent of sex when accounting for hormonal contraceptive use in females. These results draw into question oxidative stress in human disease etiology. In addition, misidentification of inflammation as oxidative stress may explain the poor responses observed in the over 180 different interventions to reduce F2-isoprostane levels across human conditions (258 references) with various degrees of success. Reexamining the true mechanism of increased F2-isoprostanes should now be a top priority.

The objective of this study was to determine whether exposing rats to ozone would result in loss of antioxidants from plasma and bronchoalveolar lavage fluid (BALF). Additional goals were to compare analyses of the same antioxidant concentration between different laboratories, to investigate which methods have the sensitivity to detect decreased levels of antioxidants, and to identify a reliable measure of oxidative stress in ozone-exposed rats. Male Fisher rats were exposed to either 2.0 ppm or 5.0 ppm ozone inhalation for 2 h. Blood plasma and BALF samples were collected 2 h, 7 h, and 16 h after the exposure. It was found that ascorbic acid in plasma collected from rats after the higher dose of ozone was lower at 2h but not later. BALF concentrations of ascorbic acid were decreased at both 2 and 7 h post-exposure. Tocopherols (α-, δ-, γ-), 5-nitro-γ-tocopherol, tocol, glutathione (GSH/GSSG) and cysteine (Cys/CySS) were not further decreased, regardless of the doses and post-exposure time points used for sample collection. Uric acid was significantly increased by the low dose at 2h and the high dose at the 7 h point, probably due to the accumulation of blood plasma in the lung from ozone-increased alveolar capillary permeability. We concluded that measurements of antioxidants in plasma are not sensitive biomarkers for oxidative damage induced by the ozone and is not a useful choice for the assessment of oxidative damage by ozone in vivo.

We studied the free radical generation involved in the development of interstitial pneumonia (IP) in an animal model of autoimmune disease. We observed an electron spin resonance (ESR) spectrum of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) radical adducts detected in the lipid extract of lungs in autoimmune-prone mice after intratracheal instillation of staphylococcal enterotoxin B. The POBN adducts detected by ESR were paralleled by infiltration of macrophages and neutrophils into the bronchoalveolar lavage fluid. To further investigate the mechanism of free radical generation, mice were pretreated with the macrophage toxicant gadolinium chloride, which significantly suppressed the radical generation. Free radical generation was also decreased by pretreatment with the xanthine oxidase (XO) inhibitor allopurinol, the iron chelator Desferal, and the inducible nitric oxide synthase (iNOS) inhibitor 1400W. Histopathologically, these drugs significantly reduced both the cell infiltration into the alveolar septal walls and the synthesis of pulmonary collagen fibers. Experiments with NADPH oxidase knockout mice showed that NADPH oxidase did not contribute to lipid radical generation. These results suggest that lipid-derived carbon-centered free radical production is important in the manifestation of IP and that a macrophage toxicant, an XO inhibitor, an iron chelator, and an iNOS inhibitor protect against both radical generation and the manifestation of IP.

Cadmium (Cd) is a toxic metal, targeting the lung, liver, kidney, and testes following acute intoxication, and causing nephrotoxicity, immunotoxicity, osteotoxicity and tumors after prolonged exposures. Reactive oxygen species (ROS) are often implicated in Cd toxicology. This minireview focused on direct evidence for the generation of free radicals in intact animals following acute Cd overload and discussed the association of ROS in chronic Cd toxicity and carcinogenesis. Cd-generated superoxide anion, hydrogen peroxide, and hydroxyl radicals in vivo have been detected by the electron spin resonance spectra, which are often accompanied by activation of redox sensitive transcription factors (e.g., NF-kappaB, AP-1 and Nrf2) and alteration of ROS-related gene expression. It is generally agreed upon that oxidative stress plays important roles in acute Cd poisoning. However, following long-term Cd exposure at environmentally-relevant low levels, direct evidence for oxidative stress is often obscure. Alterations in ROS-related gene expression during chronic exposures are also less significant compared to acute Cd poisoning. This is probably due to induced adaptation mechanisms (e.g., metallothionein and glutathione) following chronic Cd exposures, which in turn diminish Cd-induced oxidative stress. In chronic Cd-transformed cells, less ROS signals are detected with fluorescence probes. Acquired apoptotic tolerance renders damaged cells to proliferate with inherent oxidative DNA lesions, potentially leading to tumorigenesis. Thus, ROS are generated following acute Cd overload and play important roles in tissue damage. Adaptation to chronic Cd exposure reduces ROS production, but acquired Cd tolerance with aberrant gene expression plays important roles in chronic Cd toxicity and carcinogenesis.

Post-translational modification of proteins due to exposure to radicals and other reactive species are markers of metabolic and inflammatory oxidative stress such as sepsis. This study uses the nitrone spin-trap DMPO and a combination of immuno-spin trapping and mass spectrometry to identify in vivo products of radical reactions in mice. We report the detection of dose-dependent production of DMPO-carboxypeptidase B1 (CPB1) adducts in the spleens of mice treated with lipopolysaccharide (LPS). Additionally, we report significant detection of DMPO-CPB1 adducts in mice experiencing normal physiological conditions. Treatments with inhibitors and experiments with knock-out mice indicate that xanthine oxidase and endothelial nitric oxide synthase are important sources of the reactive species that lead to CPB1 adduct formation. We also report a significant loss of CPB1 activity following LPS challenge in conjunction with an increase in CPB1 protein accumulation. This suggests the presence of a possible mechanism for CPB1 activity loss with compensatory protein production.

Cadmium (Cd) is a known industrial and environmental pollutant. In the present work, an in vivo spin-trapping technique was used in conjunction with electron spin resonance (ESR) spectroscopy to investigate free radical generation in rats following administration of cadmium chloride (CdCl2, 40 micromol/kg) and the spin trapping agent alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN, 1 g/kg). In Cd-treated rats, POBN radical adducts were formed in the liver, were excreted into the bile, and exhibited an ESR spectrum consistent with a carbon-centered radical species probably derived from endogenous lipids. Isotope substitution of dimethyl sulfoxide [(CH3)2SO] with 13C demonstrated methyl radical formation (POBN/*13CH3). This adduct indicated the production of hydroxyl radical, which reacted with [(13CH3)2SO] to form *13CH3, which then reacted with POBN to form POBN/*13CH3. Depletion of hepatic glutathione by diethyl maleate significantly increased free radical production, whereas inactivation of Kupffer cells by gadolinium chloride and chelation of iron by desferal inhibited it. Treatment with the xanthine oxidase inhibitor allopurinol, the catalase inhibitor aminobenzotriazole, or the cytochrome P450 inhibitor 3-amino-1,2,4-triazole had no effect. This is the first study to show Cd generation of reactive oxygen- and carbon-centered radical species by involvement of both iron mediation through iron-catalyzed reactions and activation of Kupffer cells, the resident liver macrophages.

This study examined the role of oxidative stress in neurotoxic effects of cadmium chloride (Cd) in rat primary mid-brain neuron-glia cultures. Cd accumulated in neuron-glia cultures and produced cytotoxicity in a dose-dependent manner, with IC(50) of 2.5microM 24 h after exposure. (3)H-dopamine uptake into neuron-glia cultures was decreased 7 days after Cd exposure, with IC(50) of 0.9microM, indicative of the sensitivity of dopaminergic neurons to Cd toxicity. To investigate the role of microglia in Cd-induced toxicity to neurons, microglia-enriched cultures were prepared. Cd significantly increased intracellular reactive oxygen species production in microglia-enriched cultures, as evidenced by threefold increases in 2',7'-dichlorofluorescein signals. Using 5,5-dimethyl-1-pyrroline N-oxide as a spin-trapping agent, Cd increased electron spin resonance signals by 3.5-fold in microglia-enriched cultures. Cd-induced oxidative stress to microglia-enriched cultures was further evidenced by activation of redox-sensitive transcription factor nuclear factor kappa B and activator protein-1 (AP-1), and the increased expression of oxidative stress-related genes, such as metallothionein, heme oxygenase-1, glutathione S-transferase pi, and metal transport protein-1, as determined by gel-shift assays and real-time reverse transcription-PCR, respectively, in microglia-enriched cultures. In conclusion, Cd is toxic to neuron-glia cultures, and the oxidative stress from microglia may play important roles in Cd-induced damage to dopaminergic neurons.

The biomarker 8-iso-prostaglandin F2α (8-iso-PGF2α) is regarded as the gold standard for detection of excessive chemical lipid peroxidation in humans. However, biosynthesis of 8-iso-PGF2α via enzymatic lipid peroxidation by prostaglandin-endoperoxide synthases (PGHSs), which are significantly induced in inflammation, could lead to incorrect biomarker interpretation. To resolve the ambiguity with this biomarker, the ratio of 8-iso-PGF2α to prostaglandin F2α (PGF2α) is established as a quantitative measure to distinguish enzymatic from chemical lipid peroxidation in vitro, in animal models, and in humans. Using this method, we find that chemical lipid peroxidation contributes only 3 % to the total 8-iso-PGF2α in the plasma of rats. In contrast, the 8-iso-PGF2α levels in plasma of human males is generated >99% by chemical lipid peroxidation. This establishes the potential for an alternate pathway of biomarker synthesis, and draws into question the source of increases in 8-iso-PGF2α seen in many human diseases. In conclusion, solely measuring increases in 8-iso-PGF2α do not necessarily reflect increases in oxidative stress; therefore, past studies using 8-iso-PGF2α as a marker of oxidative stress may have been misinterpreted. The 8-iso-PGF2α/ PGF2α ratio can be used to distinguish biomarker synthesis pathways and thus confirms the potential change in oxidative stress in the myriad of disease and chemical exposures known to induce 8-iso-PGF2α.

Parkinson's disease (PD) is a debilitating, progressive, neurodegenerative disorder characterized by progressive loss of dopaminergic neurons and motor deficits. Alpha-synuclein-containing aggregates represent a feature of a variety of neurodegenerative disorders, including PD; however, the mechanism that initiates and promotes intraneuronal alpha-synuclein aggregation remains unknown. We hypothesized protein radical formation as an initiating mechanism for alpha-synuclein aggregation. Therefore, we used the highly sensitive immuno-spin trapping technique to investigate protein radical formation as a possible mechanism of alpha-synuclein aggregation as well as to investigate the source of protein radical formation in the midbrains of Maneb- and paraquat-coexposed mice. Coexposure to Maneb and paraquat for 6 weeks resulted in active microgliosis, NADPH oxidase activation, and inducible nitric oxide synthase (iNOS) induction, which culminated in protein radical formation in the midbrains of mice. Results obtained with immuno-spin trapping and immunoprecipitation experiments confirmed formation of alpha-synuclein radicals in dopaminergic neurons of exposed mice. Free radical formation requires NADPH oxidase and iNOS, as indicated by decreased protein radical formation in knockout mice (P47phox(-/-) and iNOS(-/-)) and in mice treated with inhibitors such as FeTPPS (a peroxynitrite decomposition catalyst), 1400 W (an iNOS inhibitor), or apocynin (a NADPH oxidase inhibitor). Concurrence of protein radical formation with dopaminergic neuronal death indicated a link between protein radicals and disease progression. Taken together, these results show for the first time the formation and detection of the alpha-synuclein radical and suggest that NADPH oxidase and iNOS play roles in peroxynitrite-mediated protein radical formation and subsequent neuronal death in the midbrains of Maneb- and paraquat-coexposed mice.

Oxidation products of lipids, proteins, and DNA in the blood, plasma, and urine of rats were measured as part of a comprehensive, multilaboratory validation study searching for noninvasive biomarkers of oxidative stress. This article is the second report of the nationwide Biomarkers of Oxidative Stress Study using acute CCl4 poisoning as a rodent model for oxidative stress. The time-dependent (2, 7, and 16 h) and dose-dependent (120 and 1200 mg/kg i.p.) effects of CCl4 on concentrations of lipid hydroperoxides, TBARS, malondialdehyde (MDA), isoprostanes, protein carbonyls, methionine sulfoxidation, tyrosine products, 8-hydroxy-2'-deoxyguanosine (8-OHdG), leukocyte DNA-MDA adducts, and DNA-strand breaks were investigated to determine whether the oxidative effects of CCl4 would result in increased generation of these oxidation products. Plasma concentrations of MDA and isoprostanes (both measured by GC-MS) and urinary concentrations of isoprostanes (measured with an immunoassay or LC/MS/MS) were increased in both low-dose and high-dose CCl4-treated rats at more than one time point. The other urinary markers (MDA and 8-OHdG) showed significant elevations with treatment under three of the four conditions tested. It is concluded that measurements of MDA and isoprostanes in plasma and urine as well as 8-OHdG in urine are potential candidates for general biomarkers of oxidative stress. All other products were not changed by CCl4 or showed fewer significant effects.

Plasma and urinary levels of malondialdehyde-like products (MDA) and isoprostanes were identified as markers of in vivo lipid peroxidation in an animal model of CCl4 poisoning. We sought to determine the extent to which the formation of these oxidation products is influenced by inhibition of the cyclooxygenase enzymes which catalytically generate proinflammatory lipid peroxidation products known as prostaglandins and thromboxane. In the present studies, after induction of oxidant stress in rats with CCl4, lipid peroxidation products measured in plasma and urine demonstrate that isoprostanes and MDA can be partially inhibited by cyclooxygenase inhibitors, albeit to different extents. The lowering of isoprostane and MDA formation, however, may not to due primarily to the diminution of catalytic generation of isoprostanes or MDA by the cyclooxygenases but, rather, may be the result of the suppression of nonenzymatic lipid peroxidation. This is suggested since 8,12-iso-iPF2alpha-VI is also reduced by indomethacin, yet, unlike other isoprostanes and MDA, it is not generated catalytically by the cyclooxygenase. Thus, although the two cyclooxygenase inhibitors we tested have statistically significant effects on the measurements of both isoprostanes and MDA in this study, the results provide evidence that these lipid-degradation products primarily constitute markers of oxidative stress.

When dimethyl sulfoxide (DMSO) is oxidized via hydroxyl radical (HO(.-)), it forms methyl radicals ((.-)CH(3)) that can be spin trapped and detected by electron spin resonance (ESR). This ESR spin trapping technique has been widely used in many biological systems to indicate in vivo HO(.-) formation. However, we recently reported that (.-)CH(3) might not be the only carbon-centered radical that was trapped and detected by ESR from in vivo DMSO oxidation. In the present study, newly developed combination techniques consisting of dual spin trapping (free radicals trapped by both regular and deuterated alpha-[4-pyridyl 1]-N-tert-butyl nitrone, d(0)/d(9)-POBN) followed by LC/ESR and LC/MS were used to characterize and quantify all POBN-trapped free radicals from the interaction of HO(.-) and DMSO. In addition to identifying the two well-known free radicals, (.-)CH(3) and (.-)OCH(3), from this interaction, we also characterized two additional free radicals, (.-)CH(2)OH and (.-)CH(2)S(O)CH(3). Unlike ESR, which can measure POBN adducts only in their radical forms, LC/MS identified and quantified all three redox forms, including the ESR-active radical adduct and two ESR-silent forms, the nitrone adduct (oxidized adduct) and the hydroxylamine (reduced adduct). In the bile of rats treated with DMSO and POBN, the ESR-active form of POBN/(.-)CH(3) was not detected. However, with the addition of the LC/MS technique, we found approximately 0.75 microM POBN/(.-)CH(3) hydroxylamine, which represents a great improvement in radical detection sensitivity and reliability. This novel protocol provides a comprehensive way to characterize and quantify in vitro and in vivo free radical formation and will have many applications in biological research.

Cytochrome P450 (CYP) 2E1 is induced by ethanol and is postulated to be a source of reactive oxygen species during alcoholic liver disease. However, there was no difference in liver pathology and radical formation between wild-type and CYP2E1 knockout mice fed ethanol. Other CYP isoforms may contribute these effects if CYP2E1 is inhibited or absent. The purpose of this study was, therefore, to determine if blocking most of the P450 isoforms with 1-aminobenzotriazole (ABT; 100 mg/kg i.g.), has any effect on liver damage and oxidative stress due to alcohol in rats and mice. Male C57BL/6 mice and Wistar rats were fed either high-fat control or ethanol-containing enteral diet for 4 weeks. ABT had a significant inhibitory effect on many P450 isoforms independent of concomitant alcohol administration. However, ABT did not protect against liver damage due to alcohol in either species. Indices of oxidative stress and inflammation were also similar in livers from vehicle-treated and ABT-treated animals fed ethanol. In summary, suppression of P450 activity with ABT had no apparent effect on oxidative stress caused by alcohol in both rats and mice. These data support the hypothesis that oxidative stress and liver damage can occur independently of CYP activities in both rats and mice during early alcohol-induced liver injury.

Arsenic is a human carcinogen; however, the mechanisms of arsenic's induction of carcinogenic effects have not been identified clearly. We have shown previously that monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III)) are genotoxic and can damage supercoiled phiX174 DNA and the DNA in peripheral human lymphocytes in culture. These trivalent arsenicals are biomethylated forms of inorganic arsenic and have been detected in the urine of subjects exposed to arsenite and arsenate. We show here by molecular, chemical, and physical methods that reactive oxygen species (ROS) are intermediates in the DNA-damaging activities of MMA(III) and DMA(III). Using the phiX174 DNA nicking assay we found that the ROS inhibitors Tiron, melatonin, and the vitamin E analogue Trolox inhibited the DNA-nicking activities of both MMA(III) and DMA(III) at low micromolar concentrations. The spin trap agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) also was effective at preventing the DNA nicking induced by MMA(III) and DMA(III). ESR spectroscopy studies using DMPO identified a radical as a ROS intermediate in the DNA incubations with DMA(III). This radical adduct was assigned to the DMPO-hydroxyl free radical adduct on the basis of comparison of the observed hyperfine splitting constants and line widths with those reported in the literature. The formation of the DMPO-hydroxyl free radical adduct was dependent on time and the presence of DMA(III) and was completely inhibited by Tiron and Trolox and partially inhibited by DMSO. Using electrospray mass spectrometry, micromolar concentrations of DMA(V) were detected in the DNA incubation mixtures with DMA(III). These data are consistent with the conclusions that the DNA-damaging activity of DMA(III) is an indirect genotoxic effect mediated by ROS-formed concomitantly with the oxidation of DMA(III) to DMA(V).

Intratracheal instillation of lipopolysaccharide (LPS) activates alveolar macrophages and infiltration of neutrophils, causing lung injury/acute respiratory distress syndrome. Free radicals are a special focus as the final causative molecules in the pathogenesis of lung injury caused by LPS. Although in vitro investigation has demonstrated radical generation after exposure of cells to LPS, in vivo evidence is lacking. Using electron spin resonance (ESR) and the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN), we investigated in vivo free radical production by rats treated with intratracheal instillation of LPS. ESR spectroscopy of lipid extract from lungs exposed to LPS for 6 h gave a spectrum consistent with that of a POBN/carbon-centered radical adduct (aN=14.94+/-0.07 G and abetaH=2.42+/-0.06 G) tentatively assigned as a product of lipid peroxidation. To further investigate the mechanism of LPS-initiated free radical generation, rats were pretreated with the phagocytic toxicant GdCl3, which significantly decreased the production of radical adducts with a corresponding decrease in neutrophil infiltration. NADPH oxidase knockout mice completely blocked phagocyte-mediated, ESR-detectable radical production in this model of acute lung injury. Rats treated intratracheally with LPS generate lipid-derived free radicals via activation of NADPH oxidase.

Organic peroxides are widely used in the chemical industry as initiators of oxidation for the production of polymers and fiber-reinforced plastics, in the manufacture of polyester resin coatings, and pharmaceuticals. Free radical production is considered to be one of the key factors contributing to skin tumor promotion by organic peroxides. In vitro experiments have demonstrated metal-catalyzed formation of alkoxyl, alkyl, and aryl radicals in keratinocytes incubated with cumene hydroperoxide. The present study investigated in vivo free radical generation in lipid extracts of mouse skin exposed to cumene hydroperoxide. The electron spin resonance (ESR) spin-trapping technique was used to detect the formation of alpha-phenyl-N-tert-butylnitrone (PBN) radical adducts, following intradermal injection of 180 mg/kg PBN. It was found that 30 min after topical exposure, cumene hydroperoxide (12 mmol/kg) induced free radical generation in the skin of female Balb/c mice kept for 10 weeks on vitamin E-deficient diets. In contrast, hardly discernible radical adducts were detected when cumene hydroperoxide was applied to the skin of mice fed a vitamin E-sufficient diet. Importantly, total antioxidant reserve and levels of GSH, ascorbate, and vitamin E decreased 34%, 46.5%. 27%, and 98%, respectively, after mice were kept for 10 weeks on vitamin E-deficient diet. PBN adducts detected by ESR in vitamin E-deficient mice provide direct evidence for in vivo free radical generation in the skin after exposure to cumene hydroperoxide.

This study examined the effect of acute cadmium on stress-related gene expression and free radical production in wild-type and metallothionein-I/II-null (MT-null) mice. Atlas Toxicology arrays showed that acute cadmium (40 μmol/kg as CdCl 2 , ip for 3 h) markedly increased the expression of genes encoding heat-shock proteins, heme oxygenase-1, and genes in response to DNA damage/repair. The expression of genes encoding cytochrome P450 enzymes, UDP-glucuronosyltransferases, Mn-superoxide dismutase, and catalase was suppressed by cadmium. MT-null mice were more sensitive than wild-type mice to cadmium-induced, stress-related gene expression, in accord with greater activation of transcription factor AP-1 and phosphorylated JNK and ERK. To evaluate free radical production, mice were simultaneously given the spin trap agent, N-tert -butyl-α-phenylnitrone (PBN, 250 mg in DMSO/kg, ip) with cadmium, and livers were removed 30 min later for PBN-trapped radical extraction with chloroform:methanol (2:1), and detected with electron spin resonance (ESR). Cadmium treatment caused detectable ESR signals for PBN adducts as well as lipid peroxidation in the liver similarly in both wild-type and MT-null mice. Thus, the mechanism of acute cadmium toxicity involves multiple facets including oxidative damage and aberrant gene expression, and absence of MT exacerbates Cd-induced aberrant gene expression.

Electron spin resonance spectroscopy has been used to study free radical generation in rats with acute sodium formate poisoning. The in vivo spin-trapping technique was used with α-(4-pyridyl-1-oxide)- N - t -butylnitrone (POBN), which reacts with free radical metabolites to form radical adducts, which were detected in the bile and urine samples from Fischer rats. The use of [ 13 C]-sodium formate and computer simulations of the spectra identified the 12-line spectrum as arising from the POBN/carbon dioxide anion radical adduct. The identification of POBN/ ⋅ CO \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{-}}}\end{equation*}\end{document} radical adduct provides direct electron spin resonance spectroscopy evidence for the formation of ⋅ CO \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{-}}}\end{equation*}\end{document} radicals during acute intoxication by sodium formate, suggesting a free radical metabolic pathway. To study the mechanism of free radical generation by formate, we tested several known inhibitors. Both allopurinol, an inhibitor of xanthine oxidase, and aminobenzotriazole, a cytochrome P450 inhibitor, decreased free radical formation from formate, which may imply a dependence on hydrogen peroxide. In accord with this hypothesis, the catalase inhibitor 3-aminotriazole caused a significant increase in free radical formation. The iron chelator Desferal decreased the formation of free radicals up to 2-fold. Presumably, iron plays a role in the mechanism of free radical generation by formate via the Fenton reaction. The detection of formate free radical metabolites generated in vivo and the key role of the Fenton reaction in this process may be important for understanding the pathogenesis of both formate and methanol intoxication.

The purpose of the present study was to investigate the mechanism of cross-tolerance to nickel in arsenic-transformed cells. Chronic arsenite-exposed (CAsE) cells (TRL 1215 cells, which had been continuously exposed to 0.5 microM arsenite for 20 or more weeks) and control TRL 1215 cells were both exposed to nickel for 24 h, and cell viability was determined by metabolic integrity. The LC(50) for nickel was 608 +/- 32 microM in CAsE cells as compared to 232 +/- 16 microM in control cells, a 2.6-fold increase. CAsE and control cells were treated with 200 microM nickel for 4 h and cellular-free radical production was measured using ESR spectrometry. Hydroxyl radical generation was decreased in CAsE cells. Thiobarbituric acid reactive substances, indicative of lipid peroxidation, and 8-oxo-2'-deoxyguanosine, indicative of oxidative DNA damage, were reduced in CAsE cells. Flow cytometric analysis using Annexin/FITC revealed that nickel-induced apoptosis was reduced in CAsE cells. CAsE cells showed generalized resistance to oxidant-induced toxicity as evidenced by a marked reduction in sensitivity to hydrogen peroxide. Interestingly, intracellular reduced glutathione (GSH) levels were significantly increased in CAsE cells, and when GSH was depleted, CAsE cells lost their nickel resistance. The mechanism of arsenic-induced cross-tolerance to cytotoxicity, genotoxicity, and apoptosis induced by nickel appears related to a generalized resistance to oxidant-induced injury, probably based, at least in part, in increased cellular GSH levels.

This article describes a procedure for the quantitation of the isoprostane 15-F2t-IsoP (9a,11a,15S-trihydroxy-(8b)-prosta-5Z,13E-dien-1-oic acid [CAS#27415-26-5] formerly known as 8-epi-PGF2a or 8-iso-PGF2a, and also as iPF2a-III). We have combined features from several earlier methods for 15-F2t-IsoP and prostaglandins, and identified and modified those steps that may lead to poor recoveries. The resulting protocol is precise and reliable, and was validated by a blind time-course study of plasma levels in rats treated with 120 and 1200 mg CCl4/kg body weight. Plasma levels of 15-F2t-IsoP, as measured according to the procedure described above, are good indicators of acute oxidative stress as induced by CCl4. The precision of the measurements allows detection of elevated plasma 15-F2t-IsoP levels as long as 16 h after an acute exposure of 120 mg CCl4/kg body weight, and 2 h after an exposure of 1 mg CCl4/kg body weight. The results of this low-dose, pilot study suggest that this method has sufficient analytical precision to allow the detection of the small changes in plasma isoprostane levels, which result from chronic and/or lower-level exposures to agents causing oxidative stress.

In North America, liver disease due to alcohol consumption is an important cause of death in adults, although its pathogenesis remains obscure. Despite the fact that resident hepatic macrophages are known to contribute to early alcohol-induced liver injury via oxidative stress, the exact source of free radicals has remained a mystery. To test the hypothesis that NADPH oxidase is the major source of oxidants due to ethanol, we used p47(phox) knockout mice, which lack a critical subunit of this major source of reactive oxygen species in activated phagocytes. Mice were treated with ethanol chronically, using a Tsukamoto-French protocol, for 4 weeks. In wild-type mice, ethanol caused severe liver injury via a mechanism involving gut-derived endotoxin, CD14 receptor, production of electron spin resonance-detectable free radicals, activation of the transcription factor NF-kappaB, and release of cytotoxic TNF-alpha from activated Kupffer cells. In NADPH oxidase-deficient mice, neither an increase in free radical production, activation of NF-kappaB, an increase in TNF-alpha mRNA, nor liver pathology was observed. These data strongly support the hypothesis that free radicals from NADPH oxidase in hepatic Kupffer cells play a predominant role in the pathogenesis of early alcohol-induced hepatitis by activating NF-kappaB, which activates production of cytotoxic TNF-alpha.

Metabolic activation of peroxides and hydroperoxides to free radicals is associated with the tumor promoting activity of these compounds. tert-Butyl hydroperoxide (t-BOOH) metabolism has been extensively studied as a model of peroxide biotransformation. In vivo studies are limited, and the hemoglobin-thiyl radical was the only species thus far identified in the blood of treated rats. Here we further examine t-BOOH metabolism in vivo with regard to free radical and DNA adduct production. Spin-trapping experiments with phenyl-N-tert-butylnitrone (PBN) led to the detection of EPR signals in the blood, bile, and organic extracts of the liver and stomach of rats treated with t-BOOH. Analysis of these signals demonstrated that t-BOOH metabolism in vivo produces alkyl radicals, detected in the bile and organic extracts of liver and stomach, in addition to the previously identified hemoglobin-thiyl radical. To characterize the produced alkyl radicals, experiments were performed with (13)C-labeled t-BOOH and two spin traps, PBN and alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN). The latter was used because the EPR signals obtained with PBN were too weak to be unambiguous. Nevertheless, the EPR signals present in the bile of animals treated with (13)C-labeled t-BOOH and PBN or POBN were consistent with adducts of (13)C-labeled methyl radical and an unidentified alkyl radical. The latter is probably derived from lipids oxidized by the metabolically produced primary radicals, methyl and its precursor, tert-butoxyl. The presence of 8-methylguanine and 7-methylguanine in hydrolysates of DNA from liver and stomach of rats treated with t-BOOH was also examined. 8-Methylguanine, a typical product of methyl radical attack on DNA, was detectable in both the liver and stomach of treated rats. The results may be relevant to the understanding of the genotoxic properties of other peroxides, particularly of cumene hydroperoxide.

Antioxidants in the blood plasma of rats were measured as part of a comprehensive, multilaboratory validation study searching for noninvasive biomarkers of oxidative stress. For this initial study an animal model of CCl(4) poisoning was studied. The time (2, 7, and 16 h) and dose (120 and 1200 mg/kg, intraperitoneally)-dependent effects of CCl(4) on plasma levels of alpha-tocopherol, coenzyme Q (CoQ), ascorbic acid, glutathione (GSH and GSSG), uric acid, and total antioxidant capacity were investigated to determine whether the oxidative effects of CCl(4) would result in losses of antioxidants from plasma. Concentrations of alpha-tocopherol and CoQ were decreased in CCl(4)-treated rats. Because of concomitant decreases in cholesterol and triglycerides, it was impossible to dissociate oxidation of alpha-tocopherol and the loss of CoQ from generalized lipid changes, due to liver damage. Ascorbic acid levels were higher with treatment at the earliest time point; the ratio of GSH to GSSG generally declined, and uric acid remained unchanged. Total antioxidant capacity showed no significant change except for 16 h after the high dose, when it was increased. These results suggest that plasma changes caused by liver malfunction and rupture of liver cells together with a decrease in plasma lipids do not permit an unambiguous interpretation of the results and impede detection of any potential changes in the antioxidant status of the plasma.

The continuous intragastric enteral feeding protocol in the rat was a major development in alcohol-induced liver injury (ALI) research. Much of what has been learned to date involves inhibitors or nutritional manipulations that may not be specific. Knockout technology avoids these potential problems. Therefore, we used long-term intragastric cannulation in mice to study early ALI. Reactive oxygen species are involved in mechanisms of early ALI; however, their key source remains unclear. Cytochrome P-450 (CYP)2E1 is induced predominantly in hepatocytes by ethanol and could be one source of reactive oxygen species leading to liver injury. We aimed to determine if CYP2E1 was involved in ALI by adapting the enteral alcohol (EA) feeding model to CYP2E1 knockout (−/−) mice. Female CYP2E1 wild-type (+/+) or −/− mice were given a high-fat liquid diet with either ethanol or isocaloric maltose-dextrin as control continuously for 4 wk. All mice gained weight steadily over 4 wk, and there were no significant differences between groups. There were also no differences in ethanol elimination rates between CYP2E1 +/+ and −/− mice after acute ethanol administration to naive mice or mice receiving EA for 4 wk. However, EA stimulated rates 1.4-fold in both groups. EA elevated serum aspartate aminotransferase levels threefold to similar levels over control in both CYP2E1 +/+ and −/− mice. Liver histology was normal in control groups. In contrast, mice given ethanol developed mild steatosis, slight inflammation, and necrosis; however, there were no differences between the CYP2E1 +/+ and −/− groups. Chronic EA induced other CYP families (CYP3A, CYP2A12, CYP1A, and CYP2B) to the same extent in CYP2E1 +/+ and −/− mice. Furthermore, POBN radical adducts were also similar in both groups. Data presented here are consistent with the hypothesis that oxidants from CYP2E1 play only a small role in mechanisms of early ALI in mice. Moreover, this new mouse model illustrates the utility of knockout technology in ALI research.

The anion radicals of 4-nitroquinoline N-oxide (4-NQO) and 4-nitrosoquinoline N-oxide (4-NOQO) carcinogens were detected and characterized by electron spin resonance (ESR) spectroscopy. The structures of the radical intermediates were examined by density functional theory (DFT) at the level of hybrid unrestricted uBecke3LYP. The formation of superoxide anion radical catalyzed by flavin-containing enzymes such as cytochrome P450 reductase or xanthine oxidase in the presence of 4-NQO or 4-nitroquinoline N-oxide was studied by spin-trapping experiments. In this case, the ESR signal of the 5,5-dimethyl-1-pyrroline N-oxide (DMPO)-superoxide radical adduct was observed, and its formation was inhibited by superoxide dismutase (SOD). No ESR signal was detected when the two-electron-transferring flavoenzyme DT-diaphorase (NADPH-quinone oxidoreductase) was used. The above is consistent with a one-electron reduction in the metabolism of these nitro compounds to anion free radicals by various flavoenzyme reductases.

We previously reported the detection of a carbon-centered radical adduct of alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (POBN) in the bile of rats acutely poisoned with Cr(VI) utilizing an electron spin resonance spin-trapping technique. These former studies suggested that the free radical metabolite was derived from a polyunsaturated fatty acid. The present studies were undertaken to further characterize this radical adduct and to determine whether its formation is associated with enhanced lipid peroxidation in vivo. This report demonstrates that electron spin resonance (ESR) spectra with hyperfine coupling constants aN of 15.71 G and of 2.90 G were present in bile from Cr(VI)-poisoned rats. We found out that virtually identical ESR spectra were obtained when authentic POBN-pentyl radical adducts generated from the reaction of POBN with either pentylhydrazine or linoleic or arachidonic acid with lipoxygenase were added to bile. The hyperfine coupling constants for the POBN-pentyl radical adducts added to bile were as follows: aN = 15.85 G and = 2.60 G for the reaction between pentylhydrazine and POBN; aN = 15.72 G and = 2.61 G for the reaction between arachidonic acid, lipoxygenase, and POBN; and aN = 15.85 G and = 2. 85 G for the reaction between linoleic acid, lipoxygenase, and POBN. In addition, the formation of this radical adduct was associated with lipid peroxidation as quantified by increases in F2-isoprostane levels in bile. These studies, therefore, provide additional evidence that acute Cr(VI) poisoning is associated with enhanced generation of F2-isoprostanes in vivo and tentatively identify the radical species that is produced as the POBN-pentyl radical adduct.

It has been postulated that the in vivo toxicity of asbestos results from its catalysis of free radical generation. We examined in vivo radical production using electron spin resonance (ESR) coupled with the spin trap α-(4-pyridyl-1-oxide)-N-t-butylnitrone (4-POBN); 180 day-old rats were intratracheally instilled with either 500 μg crocidolite or saline. Twenty-four hours later, histologic examination revealed a neutrophilic inflammatory response. ESR spectroscopy of the chloroform extract from lungs exposed to asbestos gave a spectrum consistent with a carbon-centered radical adduct, while those spectra from lungs instilled with saline revealed a much weaker signal. This same radical formation persisted and, even one month after instillation, could be detected in the lungs of rats exposed to asbestos. The 4-POBN adducts detected by ESR are very similar to, if not identical with, ethyl and pentyl radical adducts, providing evidence of in vivo lipid peroxidation resulting from asbestos exposure. We conclude that, after instillation of crocidolite in the rat, ESR analysis of lung tissue demonstrates in vivo free radical production.

Microglia are the resident immune cells in the brain. Microglial activation is characteristic of several inflammatory and neurodegenerative diseases including Alzheimer's disease, multiple sclerosis, and Parkinson's disease. Though lipopolysaccharide (LPS)-induced microglial activation in models of Parkinson's disease is well documented, the free radical-mediated protein radical formation and its underlying mechanism during LPS-induced microglial activation are not known. Here we have used immuno-spin trapping and RNA interference to investigate the role of inducible nitric oxide synthase (iNOS) in peroxynitrite-mediated protein radical formation in murine microglial BV2 cells treated with LPS. Treatment of BV2 cells with LPS resulted in morphological changes, induction of iNOS, and increased protein radical formation. Pretreatments with FeTPPS (a peroxynitrite decomposition catalyst), L-NAME (total NOS inhibitor), 1400W (iNOS inhibitor), and apocynin significantly attenuated LPS-induced protein radical formation and tyrosine nitration. Results obtained with coumarin-7-boronic acid, a highly specific probe for peroxynitrite detection, correlated with LPS-induced tyrosine nitration, which demonstrated involvement of peroxynitrite in protein radical formation. A similar degree of protection conferred by 1400W and L-NAME led us to conclude that only iNOS, and no other forms of NOS, is involved in LPS-induced peroxynitrite formation. Subsequently, siRNA for iNOS, the iNOS-specific inhibitor 1400W, the NF-κB inhibitor PDTC, and the p38 MAPK inhibitor SB202190 was used to inhibit iNOS directly or indirectly. Inhibition of iNOS precisely correlated with decreased protein radical formation in LPS-treated BV2 cells. The time course of protein radical formation also matched the time course of iNOS expression. Taken together, these results prove the role of iNOS in peroxynitrite-mediated protein radical formation in LPS-treated microglial BV2 cells.

Nanomaterials are being utilized in an increasing variety of manufactured goods. Because of their unique physicochemical, electrical, mechanical, and thermal properties, single-walled carbon nanotubes (SWCNTs) have found numerous applications in the electronics, aerospace, chemical, polymer, and pharmaceutical industries. Previously, we have reported that pharyngeal exposure of C57BL/6 mice to SWCNTs caused dose-dependent formation of granulomatous bronchial interstitial pneumonia, fibrosis, oxidative stress, acute inflammatory/cytokine responses, and a decrease in pulmonary function. In the current study, we used electron spin resonance (ESR) to directly assess whether exposure to respirable SWCNTs caused formation of free radicals in the lungs and in two distant organs, the heart and liver. Here we report that exposure to partially purified SWCNTs (HiPco technique, Carbon Nanotechnologies, Inc., Houston, TX, USA) resulted in the augmentation of oxidative stress as evidenced by ESR detection of α-(4-pyridyl-1-oxide)-N-tert-butylnitrone spin-trapped carbon-centered lipid-derived radicals recorded shortly after the treatment. This was accompanied by a significant depletion of antioxidants and elevated biomarkers of inflammation presented by recruitment of inflammatory cells and an increase in proinflammatory cytokines in the lungs, as well as development of multifocal granulomatous pneumonia, interstitial fibrosis, and suppressed pulmonary function. Moreover, pulmonary exposure to SWCNTs also caused the formation of carbon-centered lipid-derived radicals in the heart and liver at later time points (day 7 postexposure). Additionally, SWCNTs induced a significant accumulation of oxidatively modified proteins, increase in lipid peroxidation products, depletion of antioxidants, and inflammatory response in both the heart and the liver. Furthermore, the iron chelator deferoxamine noticeably reduced lung inflammation and oxidative stress, indicating an important role for metal-catalyzed species in lung injury caused by SWCNTs. Overall, we provide direct evidence that lipid-derived free radicals are a critical contributor to tissue damage induced by SWCNTs not only in the lungs, but also in distant organs.

Electron spin resonance (ESR) spectroscopy has been used to investigate hydroxyl radical generation in rats with chronic dietary iron loading. A secondary radical spin-trapping technique was used where hydroxyl radical forms methyl radical upon reaction with DMSO. The methyl radical was then detected by ESR spectroscopy as its adduct with the spin trap alpha-phenyl-N-t-butylnitrone (PBN). This adduct was detected in the bile of rats 10 wk after being fed an iron-loading diet and 40 min after the i.p. injection of the spin trap PBN dissolved in DMSO. Bile samples were collected into a solution of the ferrous stabilizing chelator 2,2'-dipyridyl in order to prevent the generation of radical adducts ex vivo during bile collection. Identification of the ESR spectrum of the major radical adduct as that of PBN/.CH3 provides evidence for the generation of the hydroxyl radical during iron supplementation. Desferal completely inhibited in vivo hydroxyl radical generation stimulated by high dietary iron intake. No radical adducts were detected in rats which were fed the control diet for the same period of time. This is the first evidence of hydroxyl radical generation in chronic iron-loaded rats.

Ozone exposure effect on free radical-catalyzed oxidation products of lipids, proteins, and DNA in the plasma and urine of rats was studied as a continuation of the international Biomarker of Oxidative Stress Study (BOSS) sponsored by NIEHS/NIH. The goal was to identify a biomarker for ozone-induced oxidative stress and to assess whether inconsistent results often reported in the literature might be due to the limitations of the available methods for measuring the various types of oxidative products. The time- and dose-dependent effects of ozone exposure on rat plasma lipid hydroperoxides, malondialdehyde, F2-isoprostanes, protein carbonyls, methionine oxidation, and tyrosine- and phenylalanine oxidation products, as well as urinary malondialdehyde and F2-isoprostanes were investigated with various techniques. The criterion used to recognize a marker in the model of ozone exposure was that a significant effect could be identified and measured in a biological fluid seen at both doses at more than one time point. No statistically significant differences between the experimental and the control groups at either ozone dose and time point studied could be identified in this study. Tissue samples were not included. Despite all the work accomplished in the BOSS study of ozone, no available product of oxidation in biological fluid has yet met the required criteria of being a biomarker. The current negative findings as a consequence of ozone exposure are of great importance, because they document that in complex systems, as the present in vivo experiment, the assays used may not provide meaningful data of ozone oxidation, especially in human studies.

Progression from steatosis to steatohepatitic lesions is hypothesized to require a second hit. These lesions have been associated with increased oxidative stress, often ascribed to high levels of leptin and other proinflammatory mediators. Here we have examined the role of leptin in inducing oxidative stress and Kupffer cell activation in CCl4-mediated steatohepatitic lesions of obese mice.Male C57BL/6 mice fed with a high-fat diet (60%kcal) at 16 weeks were administered CCl₄ to induce steatohepatitic lesions. Approaches included use of immuno-spin trapping for measuring free radical stress, gene-deficient mice for leptin, p47 phox, iNOS and adoptive transfer of leptin primed macrophages in vivo.Diet-induced obese (DIO) mice, treated with CCl4 increased serum leptin levels. Oxidative stress was significantly elevated in the DIO mouse liver, but not in ob/ob mice, or in DIO mice treated with leptin antibody. In ob/ob mice, leptin supplementation restored markers of free radical generation. Markers of free radical formation were significantly decreased by the peroxynitrite decomposition catalyst FeTPPS, the iNOS inhibitor 1400W, the NADPH oxidase inhibitor apocynin, or in iNOS or p47 phox-deficient mice. These results correlated with the decreased expression of TNF-alpha and MCP-1. Kupffer cell depletion eliminated oxidative stress and inflammation, whereas in macrophage-depleted mice, the adoptive transfer of leptin-primed macrophages significantly restored inflammation.These results, for the first time, suggest that leptin action in macrophages of the steatotic liver, through induction of iNOS and NADPH oxidase, causes peroxynitrite-mediated oxidative stress thus activating Kupffer cells.

In the Pseudomonas aeruginosa-induced rodent pneumonia model, it is thought that free radicals are significantly associated with the disease pathogenesis. However, until now there has been no direct evidence of free radical generation in vivo. Here we used electron spin resonance (ESR) and in vivo spin trapping with α-(4-pyridyl-1-oxide)-N-tert-butylnitrone to investigate free radical production in a murine model. We detected and identified generation of lipid-derived free radicals in vivo (a(N) =14.86 ± 0.03 G and a(H)(β) =2.48 ± 0.09 G). To further investigate the mechanism of lipid radical production, we used modulating agents and knockout mice. We found that with GdCl(3) (phagocytic toxicant), NADPH-oxidase knockout mice (Nox2(-)/(-)), allopurinol (xanthine-oxidase inhibitor) and Desferal (metal chelator), generation of lipid radicals was decreased; histopathological and biological markers of acute lung injury were noticeably improved. Our study demonstrates that lipid-derived free radical formation is mediated by NADPH-oxidase and xanthine-oxidase activation and that metal-catalysed hydroxyl radical-like species play important roles in lung injury caused by Pseudomonas aeruginosa.

Ceruloplasmin (ferroxidase) is a copper-binding protein known to promote Fe(2+) oxidation in plasma of mammals. In addition to its classical ferroxidase activity, ceruloplasmin is known to catalyze the oxidation of various substrates, such as amines and catechols. Assays based on cyclic hydroxylamine oxidation are used to quantify and detect free radicals in biological samples ex vivo and in vitro. We show here that human ceruloplasmin promotes the oxidation of the cyclic hydroxylamine 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine hydrochloride (CPH) and related probes in Chelex-treated phosphate buffer and rat serum. The reaction is suppressed by the metal chelators DTPA, EDTA, and desferal, whereas heparin and bathocuproine have no effect. Catalase or superoxide dismutase additions do not interfere with the CPH-oxidation yield, demonstrating that oxygen-derived free radicals are not involved in the CPH oxidation mediated by ceruloplasmin. Plasma samples immunodepleted of ceruloplasmin have lower levels of CPH oxidation, which confirms the role of ceruloplasmin (ferroxidase) as a biological oxidizing agent of cyclic hydroxylamines. In conclusion, we show that the ferroxidase activity of ceruloplasmin is a possible biological source of artifacts in the cyclic hydroxylamine-oxidation assay used for reactive oxygen species detection and quantification.

Although studies in chemical and biological systems have demonstrated that free radical formation is mediated by Cr(VI), no ESR evidence for the generation of free radicals in vivo has been reported. We have employed an ESR spin-trapping technique to detect an adduct of the spin trap alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN) in the bile of animals given an intragastric dose of potassium dichromate. In this study, we provide evidence for in vivo radical generation resulting from Cr(VI)-poisoned rats. Upon the administration of Cr(VI) and 4-POBN, the ESR spectrum of the radical adducts present in the bile exhibited hyperfine coupling constants aN = 15.71 G and a beta H = 2.90 G. We suggest that the radical responsible for this 4-POBN adduct is carbon-centered and derived from endogenous lipids. The radical adducts detected in the bile from Cr(VI)-treated rats are proposed to be formed and trapped in the liver and excreted into bile. This is the first report of electron spin resonance evidence for the in vivo generation of free radicals by Cr(VI).

While some studies show that carbon tetrachloride-mediated metabolic oxidative stress exacerbates steatohepatitic-like lesions in obese mice, the redox mechanisms that trigger the innate immune system and accentuate the inflammatory cascade remain unclear. Here we have explored the role of the purinergic receptor P2X7-NADPH oxidase axis as a primary event in recognizing the heightened release of extracellular ATP from CCl(4)-treated hepatocytes and generating redox-mediated Kupffer cell activation in obese mice. We found that an underlying condition of obesity led to the formation of protein radicals and posttranslational nitration, primarily in Kupffer cells, at 24h post-CCl(4) administration. The free radical-mediated oxidation of cellular macromolecules, which was NADPH oxidase and P2X7 receptor-dependent, correlated well with the release of TNF-α and MCP-2 from Kupffer cells. The Kupffer cells in CCl(4)-treated mice exhibited increased expression of MHC Class II proteins and showed an activated phenotype. Increased expression of MHC Class II was inhibited by the NADPH oxidase inhibitor apocynin , P2X7 receptor antagonist A438709 hydrochloride, and genetic deletions of the NADPH oxidase p47 phox subunit or the P2X7 receptor. The P2X7 receptor acted upstream of NADPH oxidase activation by up-regulating the expression of the p47 phox subunit and p47 phox binding to the membrane subunit, gp91 phox. We conclude that the P2X7 receptor is a primary mediator of oxidative stress-induced exacerbation of inflammatory liver injury in obese mice via NADPH oxidase-dependent mechanisms.

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Instituto Nacional de Ciencia e Tecnologia (INCT) Redoxoma National Institute of Environmental Health Sciences (NIEHS) Acetoacetate (AA) and 2-methylacetoacetate (MAA) are accumulated in metabolic disorders such as diabetes and isoleucinemia. Here we examine the mechanism of AA and MAA aerobic oxidation initiated by myoglobin (Mb)/H2O2. We propose a chemiluminescent route involving a dioxetanone intermediate whose thermolysis yields triplet alpha-dicarbonyl species (methylglyoxal and diacetyl). the observed ultraweak chemiluminescence increased linearly on raising the concentration of either Mb (10-500 mu M) or AA (10-100 mM). Oxygen uptake studies revealed that MAA is almost a 100-fold more reactive than AA. EPR spin-trapping studies with MNP/MAA revealed the intermediacy of an alpha-carbon-centered radical and acetyl radical. the latter radical, probably derived from triplet diacetyl, is totally suppressed by sorbate, a well-known quencher of triplet carbonyls. Furthermore, an EPR signal assignable to MNP-AA(center dot) adduct was observed and confirmed by isotope effects. Oxygen consumption and a-dicarbonyl yield were shown to be dependent on AA or MAA concentrations (1-50 mM) and on H2O2 or tert-butOOH added to the Mb-containing reaction mixtures. That ferrylMb is involved in a peroxidase cycle acting on the substrates is suggested by the reaction pH profiles and immunospin-trapping experiments. the generation of radicals and triplet dicarbonyl products by Mb/H2O2/beta-ketoacids may contribute to the adverse health effects of ketogenic unbalance. (C) 2011 Elsevier Inc. All rights reserved. Universidade Federal de São Paulo, Dept Ciencias Exatas & Terra, Inst Ciencias Ambientais Quim & Farmaceut, BR-00972270 Diadema, SP, Brazil Univ São Paulo, Inst Quim, Dept Bioquim, BR-01498 São Paulo, Brazil Natl Inst Environm Hlth Sci, Free Rad Metab Grp, Lab Toxicol & Pharmacol, NIH, Res Triangle Pk, NC 27709 USA Universidade Federal de São Paulo, Dept Ciencias Exatas & Terra, Inst Ciencias Ambientais Quim & Farmaceut, BR-00972270 Diadema, SP, Brazil Web of Science

The electron spin resonance (ESR) spin trapping technique was employed to study the role of Cu(II) in the generation of hydroxyl radical during paraquat (PQ2+) intoxication in rats. A secondary radical trapping technique was used for the detection of hydroxyl radical generated in vivo during copper-mediated PQ2+ toxicity. According to this technique (Burkitt and Mason, Proc. Natl. Acad. Sci. USA 88, 8440-8444, 1991), the hydroxyl radical generated reacts with dimethyl sulfoxide (DMSO) in vivo to form the methyl radical, which is then spin trapped by phenyl-N-tert-butylnitrone (PBN). The relatively stable methyl radical adduct of PBN was detected in the bile of rats 2 hr after treatment with simultaneous doses of CuSO4, PQ2+, PBN, and DMSO, whereas no radical adducts were detected in the absence of administered PQ2+. Bile samples were collected into Cu(I)- and Fe(II)-stabilizing agents in order to prevent the occurrence of radical adducts generated ex vivo in bile during its collection. The analysis of radical adducts excreted via the biliary route provide strong ESR evidence for the generation of the hydroxyl radical as a result of the known futile enzymatic redox cycling of PQ2+, with copper playing an essential mediatory role. No radical adducts were detected when either CuSO4 or PQ2+ was excluded. From a different perspective, in vivo copper-dependent hydroxyl radical generation could be said to be promoted by PQ2+. This is the first report of ESR evidence for this synergetic hydroxyl radical generation by copper and PQ2+ in a whole animal.

Eosinophil peroxidase (EPO) is an abundant heme protein in eosinophils that catalyzes the formation of cytotoxic oxidants implicated in asthma, allergic inflammatory disorders, and cancer. It is known that some proteins with peroxidase activity (horseradish peroxidase and prostaglandin hydroperoxidase) can catalyze oxidation of bisulfite (hydrated sulfur dioxide), leading to the formation of sulfur trioxide anion radical ((.)SO(3)(-)). This free radical further reacts with oxygen to form peroxymonosulfate anion radical ((-)O(3)SOO(.)) and the very reactive sulfate anion radical (SO(4)()), which is nearly as strong an oxidant as the hydroxyl radical. However, the ability of EPO to generate reactive sulfur radicals has not yet been reported. Here we demonstrate that eosinophil peroxidase/H(2)O(2) is able to oxidize bisulfite, ultimately forming the sulfate anion radical (SO(4)()), and that these reactive intermediates can oxidize target proteins to protein radicals, thereby initiating protein oxidation. We used immuno-spin trapping and confocal microscopy to study protein oxidation by EPO/H(2)O(2) in the presence of bisulfite in a pure enzymatic system and in human promyelocytic leukemia HL-60 clone 15 cells, maturated to eosinophils. Polyclonal antiserum raised against the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) detected the presence of DMPO covalently attached to the proteins resulting from the DMPO trapping of protein free radicals. We found that sulfite oxidation mediated by EPO/H(2)O(2) induced the formation of radical-derived DMPO spin-trapped human serum albumin and, to a lesser extent, of DMPO-EPO. These studies suggest that EPO-dependent oxidative damage may play a role in tissue injury in bisulfite-exacerbated eosinophilic inflammatory disorders.