Site-specific carboxypeptidase B1 tyrosine nitration and pathophysiological implications following its physical association with nitric oxide synthase-3 in experimental sepsis

Regulation, Activation and Function of Caspase-11 during Health and Disease

Caspase-11 is a pro-inflammatory enzyme that is stringently regulated during its expression and activation. As caspase-11 is not constitutively expressed in cells, it requires a priming step for its upregulation, which occurs following the stimulation of pathogen and cytokine receptors. Once expressed, caspase-11 activation is triggered by its interaction with lipopolysaccharide (LPS) from Gram-negative bacteria. Being an initiator caspase, activated caspase-11 functions primarily through its cleavage of key substrates. Gasdermin D (GSDMD) is the primary substrate of caspase-11, and the GSDMD cleavage fragment generated is responsible for the inflammatory form of cell death, pyroptosis, via its formation of pores in the plasma membrane. Thus, caspase-11 functions as an intracellular sensor for LPS and an immune effector. This review provides an overview of caspase-11—describing its structure and the transcriptional mechanisms that govern its expression, in addition to its activation, which is reported to be regulated by factors such as guanylate-binding proteins (GBPs), high mobility group box 1 (HMGB1) protein, and oxidized phospholipids. We also discuss the functional outcomes of caspase-11 activation, which include the non-canonical inflammasome, modulation of actin dynamics, and the initiation of blood coagulation, highlighting the importance of inflammatory caspase-11 during infection and disease.

Toxicity of polycyclic aromatic hydrocarbons involves NOX2 activation

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PAHs cause decrease in cell viability and increase in lactate levels.

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The mixture of PAHs suppress S phase.

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Toxicity is accompanied by NOX2 activation.

Polycyclic Aromatic Hydrocarbons (PAHs) are environmental pollutants.

The present study compares the toxic effects of BaP alone and a mixture of PAHs on human breast cancer cells. We hypothesize that PAH mixture is more toxic than BaP alone, and an increased NOX2 activation is related to PAH-induced oxidative stress. Initially, we exposed cultured human breast cancer cells to BaP alone (125 ng/mL and 500 ng/mL) and a mixture of PAHs (125 ng/mL and 500 ng/mL). After 24 h of exposure, the PAH mixture demonstrated a significant (P < 0.05) reduction in cell viability. The higher concentration of BaP alone (500 ng/mL) and both 125 ng/mL and 500 ng/mL PAH mixture significantly (P < 0.05) increased lactate production by MDA-MB-231 cells. We had observed an identical level of increased lactate levels when the cells were exposed to PAHs for 48 h. Flow cytometric analysis revealed that only PAHs mixture (both 125 ng/mL and 500 ng/mL) suppressed S phase significantly (P < 0.05). Finally, immunofluorescence microscopy was undertaken to examine the role of NOX2 due to PAHs toxicity. Colocalization of GP91phox and P47phox, a hallmark of NOX2 activation in the cell membrane of macrophage Kupffer cells demonstrated that higher concentration of BaP or PAH mixture showed increased colocalization events. These data suggest that the mixture of PAHs is more toxic and perturbing to DNA synthesis than BaP alone in cultured cells, and the toxicity is accompanied by NOX2 activation. Thus PAHs can lead to the increased burden of oxidative stress and alter the cellular redox status.

Genetically Encoded Protein Tyrosine Nitration in Mammalian Cells

Tyrosine nitration has served as a major biomarker for oxidative stress and is present in high abundance in over 50 disease pathologies in humans. While data mounts on specific disease pathways from specific sites of tyrosine nitration, the role of these modifications is still largely unclear. Strategies for installing site-specific tyrosine nitration in target proteins in eukaryotic cells, through routes not dependent on oxidative stress, would provide a powerful method to address the consequences of tyrosine nitration. Developed here is a Methanosarcina barkeri aminoacyl-tRNA synthetase/tRNA pair that efficiently incorporates nitrotyrosine site-specifically into proteins in mammalian cells. We demonstrate the utility of this approach to produce nitrated proteins identified in disease conditions by producing site-specific nitroTyr-containing manganese superoxide dismutase and 14-3-3 proteins in eukaryotic cells.

Multiorgan Development of Oxidative and Nitrosative Stress in LPS-Induced Endotoxemia in C57Bl/6 Mice: DHE-Based In Vivo Approach

Detection of free radicals in tissues is challenging. Most approaches rely on incubating excised sections or homogenates with reagents, typically at supraphysiologic oxygen tensions, to finally detect surrogate, nonspecific end products. In the present work, we explored the potential of using intravenously (i.v.) injected dihydroethidine (DHE) to detect superoxide radical (O₂ ^∙-) abundance in vivo by quantification of the superoxide-specific DHE oxidation product, 2-hydroxyethidium (2-OH-E⁺), as well as ethidium (E⁺) and DHE in multiple tissues in a murine model of endotoxemia induced by lipopolysaccharide (LPS). LPS was injected intraperitoneally (i.p.), while DHE was delivered via the tail vein one hour before sacrifice. Tissues (kidney, lung, liver, and brain) were harvested and subjected to HPLC/fluorescent analysis of DHE and its monomeric oxidation products. In parallel, electron spin resonance (EPR) spin trapping was used to measure nitric oxide (^∙NO) production in the aorta, lung, and liver isolated from the same mice. Endotoxemic inflammation was validated by analysis of plasma biomarkers. The concentration of 2-OH-E⁺ varied in the liver, lung, and kidney; however, the ratios of 2-OH-E⁺/E⁺ and 2-OH-E⁺/DHE were increased in the liver and kidney but not in the lung or the brain. An LPS-induced robust level of ^∙NO burst was observed in the liver, whereas the lung demonstrated a moderate yet progressive increase in the rate of ^∙NO production. Interestingly, endothelial dysfunction was observed in the aorta, as evidenced by decreased ^∙NO production 6 hours post-LPS injection that coincided with the inflammatory burden of endotoxemia (e.g. elevated serum amyloid A and prostaglandin E₂). Combined, these data demonstrate that systemic delivery of DHE affords the capacity to specifically detect O₂ ^∙- production in vivo. Furthermore, the ratio of 2-OH-E⁺/E⁺ oxidation products in tissues provides a tool for comparative insight into the oxidative environments in various organs. Based on our findings, we demonstrate that the endotoxemic liver is susceptible to both O₂ ^∙--mediated and nonspecific oxidant stress as well as nitrosative stress. Oxidant stress in the lung was detected to a lesser extent, thus underscoring a differential response of liver and lung to endotoxemic injury induced by intraperitoneal LPS injection.

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.

High circulatory leptin mediated NOX-2-peroxynitrite-miR21 axis activate mesangial cells and promotes renal inflammatory pathology in nonalcoholic fatty liver disease

High circulatory insulin and leptin followed by underlying inflammation are often ascribed to the ectopic manifestations in non-alcoholic fatty liver disease (NAFLD) but the exact molecular pathways remain unclear. We have shown previously that CYP2E1-mediated oxidative stress and circulating leptin in NAFLD is associated with renal disease severity. Extending the studies, we hypothesized that high circulatory leptin in NAFLD causes renal mesangial cell activation and tubular inflammation via a NOX2 dependent pathway that upregulates proinflammatory miR21. High-fat diet (60% kcal) was used to induce fatty liver phenotype with parallel insulin and leptin resistance. The kidneys were probed for mesangial cell activation and tubular inflammation that showed accelerated NASH phenotype and oxidative stress in the liver. Results showed that NAFLD kidneys had significant increases in α-SMA, a marker of mesangial cell activation, miR21 levels, tyrosine nitration and renal inflammation while they were significantly decreased in leptin and p47 phox knockout mice. Micro RNA21 knockout mice showed decreased tubular immunotoxicity and proinflammatory mediator release. Mechanistically, use of NOX2 siRNA or apocynin,phenyl boronic acid (FBA), DMPO or miR21 antagomir inhibited leptin primed-miR21-mediated mesangial cell activation in vitro suggesting a direct role of leptin-mediated NOX-2 in miR21-mediated mesangial cell activation. Finally, JAK-STAT inhibitor completely abrogated the mesangial cell activation in leptin-primed cells suggesting that leptin signaling in the mesangial cells depended on the JAK-STAT pathway. Taken together the study reports a novel mechanistic pathway of leptin-mediated renal inflammation that is dependent on NOX-2-miR21 axis in ectopic manifestations underlying NAFLD-induced co-morbidities.

Xanthine oxidase inhibitors and sepsis

Xanthine oxidase activation occurs in sepsis and results in the generation of uric acid (UrAc) and reactive oxygen species (ROS). We aimed to evaluate the effect of xanthine oxidase inhibitors (XOis) in rats stimulated with lipopolysaccharide (LPS). LPS (10 mg/kg) was administered intraperitoneally (i.p.) immediately after allopurinol (Alo, 2 mg/kg) or febuxostat (Feb, 1 mg/kg) every 24 h for 3 days. To increase UrAc levels, oxonic acid (Oxo) was administered by gavage (750 mg/kg per day) for 5 days. Animals were divided into the following 10 groups (n = 6 each): (1) Control, (2) Alo, (3) Feb, (4) LPS, (5) LPSAlo, (6) LPSFeb, (7) Oxo, (8) OxoLPS, (9) OxoLPSAlo, and (10) OxoLPSFeb. Feb with or without Oxo did not aggravate sepsis. LPS administration (with or without Oxo) significantly decreased the creatinine clearance (ClCr) in LPSAlo (60%, P < 0.01) versus LPS (44%, P < 0.05) and LPSFeb (35%, P < 0.05). Furthermore, a significant increase in mortality was observed with LPSAlo (28/34, 82%) compared to LPS treatment alone (10/16, 63%) and LPSFeb (11/17, 65%, P < 0.05). In addition, increased levels of thiobarbituric acid reactive substances (TBARS), tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-10 were observed at 72 h compared to the groups that received LPS and LPSFeb with or without Oxo. In this study, coadministration of Alo in LPS-induced experimental sepsis aggravated septic shock, leading to mortality, renal function impairment, and high ROS and proinflammatory IL levels. In contrast, administration of Feb did not potentiate sepsis, probably because it did not interfere with other metabolic events.

Phosphorylation of carboxypeptidase B1 protein regulates β-cell proliferation

A reduction in pancreatic islet β-cells leads to the onset of diabetes. Hence, the identification of the mechanisms inducing β-cell proliferation is important for developing a treatment course against the disease. It has been well established that post-translational modifications (PTMs) of proteins affect their functionality. In addition, PTMs have been suggested to play important roles in organ regeneration. Therefore, in this study, we investigated PTMs associated with pancreatic regeneration using two-dimensional electrophoresis. Four carboxypeptidase B1 (CPB1) proteins were identified at different isoelectric points, with the same molecular weight. The motif of CPB1 PTMs was identified by mass spectrophotometry, and the downregulation of CPB1 phosphorylation in pancreatectomy was confirmed. The dephosphorylation of CPB1 induced β-cell proliferation. We thus surmise that the altered PTM of CPB1 is associated with pancreatic regeneration.

Identification of oxidative modifications of hemopexin and their predicted physiological relevance

Hemopexin protects against heme toxicity in hemolytic diseases and conditions, sepsis, and sickle cell disease. This protection is sustained by heme-hemopexin complexes in biological fluids that resist oxidative damage during heme-driven inflammation. However, apo-hemopexin is vulnerable to inactivation by reactive nitrogen (RNS) and oxygen species (ROS) that covalently modify amino acids. The resultant nitration of amino acids is considered a specific effect reflecting biological events. Using LC-MS, we discovered low endogenous levels of tyrosine nitration in the peptide YYCFQGNQFLR in the heme-binding site of human hemopexin, which was similarly nitrated in rabbit and rat hemopexins. Immunoblotting and selective reaction monitoring were used to quantify tyrosine nitration of in vivo samples and when hemopexin was incubated in vitro with nitrating nitrite/myeloperoxidase/glucose oxidase. Significantly, heme binding by hemopexin declined as tyrosine nitration proceeded in vitro Three nitrated tyrosines reside in the heme-binding site of hemopexin, and we found that one, Tyr-199, interacts directly with the heme ring D propionate. Investigating the oxidative modifications of amino acids after incubation with tert-butyl hydroperoxide and hypochlorous acid in vitro, we identified additional covalent oxidative modifications on four tyrosine residues and one tryptophan residue of hemopexin. Importantly, three of the four modified tyrosines, some of which have more than one modification, cluster in the heme-binding site, supporting a hierarchy of vulnerable amino acids. We propose that during inflammation, apo-hemopexin is nitrated and oxidated in niches of the body containing activated RNS- and ROS-generating immune and endothelial cells, potentially impairing hemopexin's protective extracellular antioxidant function.

Complement pathway amplifies caspase-11-dependent cell death and endotoxin-induced sepsis severity

Caspase-11–dependent cell death is controlled by carboxypeptidase B1 by inducing the cleavage of C3 and activation of C3aR.

Cell death and release of proinflammatory mediators contribute to mortality during sepsis. Specifically, caspase-11–dependent cell death contributes to pathology and decreases in survival time in sepsis models. Priming of the host cell, through TLR4 and interferon receptors, induces caspase-11 expression, and cytosolic LPS directly stimulates caspase-11 activation, promoting the release of proinflammatory cytokines through pyroptosis and caspase-1 activation. Using a CRISPR-Cas9–mediated genome-wide screen, we identified novel mediators of caspase-11–dependent cell death. We found a complement-related peptidase, carboxypeptidase B1 (Cpb1), to be required for caspase-11 gene expression and subsequent caspase-11–dependent cell death. Cpb1 modifies a cleavage product of C3, which binds to and activates C3aR, and then modulates innate immune signaling. We find the Cpb1–C3–C3aR pathway induces caspase-11 expression through amplification of MAPK activity downstream of TLR4 and Ifnar activation, and mediates severity of LPS-induced sepsis (endotoxemia) and disease outcome in mice. We show C3aR is required for up-regulation of caspase-11 orthologues, caspase-4 and -5, in primary human macrophages during inflammation and that c3aR1 and caspase-5 transcripts are highly expressed in patients with severe sepsis; thus, suggesting that these pathways are important in human sepsis. Our results highlight a novel role for complement and the Cpb1–C3–C3aR pathway in proinflammatory signaling, caspase-11 cell death, and sepsis severity.

Mass spectrometry analysis of nitrotyrosine-containing proteins

Oxidative stress plays important roles in a wide range of diseases such as cancer, inflammatory disease, neurodegenerative disorders, etc. Tyrosine nitration in a protein is a chemically stable oxidative modification, and a marker of oxidative injuries. Mass spectrometry (MS) is a key technique to identify nitrotyrosine-containing proteins and nitrotyrosine sites in endogenous and synthetic nitroproteins and nitropeptides. However, in vivo nitrotyrosine-containing proteins occur with extreme low-abundance to severely challenge the use of MS to identify in vivo nitroproteins and nitrotyrosine sites. A preferential enrichment of nitroproteins and/or nitropeptides is necessary before MS analysis. Current enrichment methods include immuno-affinity techniques, chemical derivation of the nitro group plus target isolations, followed with tandem mass spectrometry analysis. This article reviews the MS techniques and pertinent before-MS enrichment techniques for the identification of nitrotyrosine-containing proteins. This article reviews future trends in the field of nitroproteomics, including quantitative nitroproteomics, systems biological networks of nitroproteins, and structural biology study of tyrosine nitration to completely clarify the biological functions of tyrosine nitration.

Mass spectrometry and 3-nitrotyrosine: strategies, controversies, and our current perspective

Reactive-nitrogen species (RNS) such as peroxynitrite (ONOO(-)), that is, the reaction product of nitric oxide ((•)NO) and superoxide (O2(-•)), nitryl chloride (NO2Cl) and (•)NO2 react with the activated aromatic ring of tyrosine to form 3-nitrotyrosine. This modification, which has been known for more than a century, occurs to both the free form of the amino acid (i.e., soluble/free tyrosine) and to tyrosine residues covalently bound within the backbone of peptides and proteins. Nitration of tyrosine is thought to be of biological significance and has been linked to health and disease, but determining its role has proved challenging. Several key questions have been the focus of much of the research activity: (a) to what extent is free/soluble tyrosine nitrated in biological tissues and fluids, and (b) are there specific site(s) of nitration within peptides/proteins and to what extent (i.e., stoichiometry) does this modification occur? These issues have been addressed in a wide range of sample types (e.g., blood, urine, CSF, exhaled breath condensate and various tissues) and a diverse array of physiological/pathophysiological scenarios. The accurate determination of nitrated tyrosine is, however, a stumbling block. Despite extensive study, the extent to which nitration occurs in vivo, the specificity of the nitration reaction, and its importance in health and disease, remain unclear. In this review, we highlight the analytical challenges and discuss the approaches adopted to address them. Mass spectrometry, in combination with either gas chromatography (GC-MS, GC-MS/MS) or liquid chromatography (LC-MS/MS), has played the central role in the analysis of 3-nitrotyrosine and tyrosine-nitrated biological macromolecules. We discuss its unique attributes and highlight the role of stable-isotope labeled 3-nitrotyrosine analogs in both accurate quantification, and in helping to define the biological relevance of tyrosine nitration. We show that the application of sophisticated mass spectrometric techniques is advantageous if not essential, but that this alone is by no means a guarantee of accurate findings. We discuss the important analytical challenges in quantifying 3-nitrotyrosine, possible workarounds, and we attempt to make sense of the disparate findings that have been reported so far.

In vivo detection of free radicals in mouse septic encephalopathy using molecular MRI and immuno-spin trapping

Free radicals are known to play a major role in sepsis. Combined immuno-spin trapping and molecular magnetic resonance imaging (MRI) was used to detect in vivo and in situ levels of free radicals in murine septic encephalopathy after cecal ligation and puncture (CLP). DMPO (5,5-dimethyl pyrroline N-oxide) was injected over 6h after CLP, before administration of an anti-DMPO probe (anti-DMPO antibody bound to albumin-gadolinium-diethylene triamine pentaacetic acid-biotin MRI targeting contrast agent). In vitro assessment of the anti-DMPO probe in oxidatively stressed mouse astrocytes significantly decreased T1 relaxation (p < 0.0001) compared to controls. MRI detected the presence of anti-DMPO adducts via a substantial decrease in %T1 change within the hippocampus, striatum, occipital, and medial cortex brain regions (p < 0.01 for all) in septic animals compared to shams, which was sustained for over 60 min (p < 0.05 for all). Fluorescently labeled streptavidin was used to target the anti-DMPO probe biotin, which was elevated in septic brain, liver, and lungs compared to sham. Ex vivo DMPO adducts (qualitative) and oxidative products, including 4-hydroxynonenal and 3-nitrotyrosine (quantitative, p < 0.05 for both), were elevated in septic brains compared to shams. This is the first study that has reported on the detection of in vivo and in situ levels of free radicals in murine septic encephalopathy.

Effect of nitric oxide on the anticancer activity of the topoisomerase-active drugs etoposide and adriamycin in human melanoma cells

Nitric oxide (·NO) was originally identified as an innate cytotoxin. However, in tumors it can enhance resistance to chemotherapy and exacerbate cancer progression. Our previous studies indicated that (·NO/·NO-derived species react with etoposide (VP-16) in vitro and form products that show significantly reduced activity toward HL60 cells and lipopolysaccharide (LPS)-induced macrophages. Here, we further confirm the hypothesis that (÷)NO generation contributes to VP-16 resistance by examining interactions of ·NO with VP-16 in inducible nitric-oxide synthase (iNOS)-expressing human melanoma A375 cells. Inhibition of iNOS catalysis by N(6)-(1-iminoethyl)-L-lysine dihydrochloride (L-NIL) in human melanoma A375 cells reversed VP-16 resistance, leading to increased DNA damage and apoptosis. Furthermore, we found that coculturing A375 melanoma cells with LPS-induced macrophage RAW cells also significantly reduced VP-16 cytotoxicity and DNA damage in A375 cells. We also examined the interactions of (·)NO with another topoisomerase active drug, Adriamycin, in A375 cells. In contrast, to VP-16, (·)NO caused no significant modulation of cytotoxicity or Adriamycin-dependent apoptosis, suggesting that (⋅)NO does not interact with Adriamycin. Our studies support the hypothesis that (·)NO oxidative chemistry can detoxify VP-16 through direct nitrogen oxide radical attack. Our results provide insights into the pharmacology and anticancer mechanisms of VP-16 that may ultimately contribute to increased resistance, treatment failure, and induction of secondary leukemia in VP-16-treated patients.

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.

Leptin is key to peroxynitrite-mediated oxidative stress and Kupffer cell activation in experimental non-alcoholic steatohepatitis

BACKGROUND & AIMS

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Role of nitric oxide in the chemistry and anticancer activity of etoposide (VP-16,213)

Originally identified as an innate cytotoxin, nitric oxide ((·)NO) formation in tumors can influence chemotherapy and exacerbate cancer progression. Here, we examined the hypothesis that (·)NO generation contributes to cancer cell drug resistance toward the widely used anticancer drug Etoposide (VP-16). The UV-vis spectrum of VP-16 was not changed by exposure of VP-16 to (·)NO in aqueous buffer. In contrast, reddish-orange compound(s) characteristic of o-quinone- and nitroso-VP-16 were readily generated in a hydrophobic medium (chloroform) in an oxygen-dependent manner. Similar products were also formed when the VP-16 radical, generated from VP-16 and horseradish peroxidase/H2O2, was exposed directly to (·)NO in chloroform in the presence of oxygen. Separation and spectral analysis of VP-16 reaction extracts by electron spin resonance and UV-vis indicated the generation of the phenoxy radical and the o-quinone of VP-16, as well as putative nitroxide, iminoxyl, and other nitrogen oxide intermediates. Nitric oxide products of VP-16 displayed significantly diminished topoisomerase II-dependent cleavage of DNA and cytotoxicity to human HL-60 leukemia cells. LPS-mediated induction of nitric oxide synthase in murine macrophages resulted in VP-16 resistance compared to Raw cells. Furthermore, (·)NO products derived from iNOS rapidly reacted with VP-16 leading to decreased DNA damage and cytotoxicity. Together, these observations suggest that the formation of (·)NO in tumors (associated macrophages) can contribute to VP-16 resistance via the detoxification of VP-16.

Conversion of 3-nitrotyrosine to 3-aminotyrosine residues facilitates mapping of tyrosine nitration in proteins by electrospray ionization-tandem mass spectrometry using electron capture dissociation

Protein tyrosine nitration is associated with oxidative stress and various human diseases. Tandem mass spectrometry has been the method of choice for the identification and localization of this posttranslational modification to understand the underlying mechanisms and functional consequences. Due to the electron predator effect of the nitro group limiting fragmentation of the peptide backbone, electron-based dissociation has not been applicable, however, to nitrotyrosine-containing peptides. A straightforward conversion of the nitrotyrosine to the aminotyrosine residues is introduced to address this limitation. When tested with nitrated ubiquitin and human serum albumin as model proteins in top-down and bottom-up approaches, respectively, this chemical derivatization enhanced backbone fragmentation of the corresponding nitroproteins and nitropeptides by electron capture dissociation (ECD). Increased sequence coverage has been obtained by combining in the bottom-up strategy the conversion of nitrotyrosine to aminotyrosine and introducing, in addition to trypsin, a further digesting enzyme of complementary specificity, when protein nitration was mapped by liquid chromatography-electrospray ionization tandem mass spectrometry using both collision-induced dissociation (CID) and ECD.

Effect of steroid and antibiotic treatment during assisted hatching on IVF outcomes

There are limited data on the use of steroids and antibiotics in assisted reproductive technology (ART). Our aim was to evaluate the impact of these treatments on the outcome of IVF cycles in which Assisted Hatching (AH) was performed. We studied a retrospective cohort in a large university-affiliated infertility centre. Data from 1126 AH cycles performed between 2007 and 2009 were reviewed. Cycles were categorized as "treatment" (n = 640) and "no treatment" (n = 486), depending on whether they received steroids and antibiotics. The primary outcome was live birth. Secondary outcomes included implantation, spontaneous abortion, biochemical, clinical and ectopic pregnancy. Logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (CI). OR were adjusted (AOR) for age, BMI, baseline FSH, peak estradiol, cycle number, number of oocytes retrieved, number of embryos that underwent AH, number of high-implantation potential embryos, number of embryos transferred and physician in charge. The AOR (95% CI) of live birth was 1.91 (1.08-3.38), of clinical pregnancy, 1.75 (1.08-2.83) and of biochemical pregnancy, 0.24 (0.07-0.85). Our study suggests that treatment with steroids and antibiotics during AH cycles significantly increases the odds of live birth.

P2X7 receptor-NADPH oxidase axis mediates protein radical formation and Kupffer cell activation in carbon tetrachloride-mediated steatohepatitis in obese mice

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.

Kaposi's sarcoma-associated herpesvirus-encoded latency-associated nuclear antigen reduces interleukin-8 expression in endothelial cells and impairs neutrophil chemotaxis by degrading nuclear p65

Latency-associated nuclear antigen 1 (LANA-1) of Kaposi's sarcoma-associated herpesvirus (KSHV) is the major viral latent protein and functions as a multifaceted protein. Here, we report that LANA-1 attenuates the endothelial response to tumor necrosis factor alpha (TNF-α) stimulation and inhibits consequent neutrophil chemotaxis. Reporter assays showed that LANA-1 constantly repressed nuclear factor (NF)-κB transactivity upon TNF-α stimulation. We also found that LANA-1 decreased nuclear p65 protein levels through enhancement of polyubiquitylation-mediated p65 degradation and that an elongin B/elongin C-cullin 5-LANA-1-p65 complex assembled by LANA-1 was responsible for this enhanced p65 degradation. In telomerase-immortalized human umbilical vein endothelial cells, LANA-1 was demonstrated to repress interleukin-8 expression, which was involved in neutrophil recruitment to the inflammatory site. Through an in vitro transmigration assay, we determined a suppressive effect of LANA-1 on neutrophil chemotaxis. Our work suggests that KSHV LANA-1 is a negative modulator of acute inflammation and sheds light on a new mechanism by which KSHV during the latent life cycle evades the host innate immune response.

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.

Confident identification of 3-nitrotyrosine modifications in mass spectral data across multiple mass spectrometry platforms

3-nitrotyrosine (3NT) is an oxidative posttranslational modification associated with many diseases. Determining the specific sites of this modification remains a challenge due to the low stoichiometry of 3NT modifications in biological samples. Mass spectrometry-based proteomics is a powerful tool for identifying 3NT modifications, however several reports identifying 3NT sites were later demonstrated to be incorrect, highlighting that both the accuracy and efficiency of these workflows need improvement. To advance our understanding of the chromatographic and spectral properties of 3NT-containing peptides we have adapted a straightforward, reproducible procedure to generate a large set of 3NT peptides by chemical nitration of a defined, commercially available 48 protein mixture. Using two complementary LC-MS/MS platforms, a QTOF (QSTAR Elite) and dual pressure ion trap mass spectrometer (LTQ Velos), we detected over 200 validated 3NT-containing peptides with significant overlap in the peptides detected by both systems. We investigated the LC-MS/MS properties for each peptide manually using defined criteria and then assessed their utility to confirm that the peptide was 3NT modified. This broad set of validated 3NT-containing peptides can be utilized to optimize mass spectrometric instrumentation and data mining strategies or further develop 3NT peptide enrichment strategies for this biologically important, oxidative posttranslational modification.