Gas chromatographic-tandem mass spectrometric quantification of free 3-nitrotyrosine in human plasma at the basal state

A Simplified Approach for the Aqueous Synthesis of Luminescent CdSe/ZnS Core/Shell Quantum Dots and Their Applications in Ultrasensitive Determination of the Biomarker 3-Nitro-l-tyrosine

In contrast to the hot-injection organometallic routes, synthesizing stable and highly luminescent core/shell nanocrystals with encapsulation of biocompatible groups through an aqueous route is a long-standing challenge. In recent years, relatively high quantum efficiency and unique properties of core/shell nanostructured materials (quantum dots) have contributed toward enhancement in sensing capability. The present work reports a facile aqueous synthesis process of core/shell CdSe/ZnS quantum dots (QDs) with encapsulation of glutathione (GSH). The optimal conditions for the synthesis of the most stable particles were ascertained, and the different experimental analyses suggest that the stable core/shell QDs in question have good crystallinity with a size around 4.7 nm with a shell thickness of 0.7 nm and a photoluminescence quantum yield of about 35%. Further, it is demonstrated that the as-synthesized material has great potential in detecting as low as 0.28 nM 3-nitro-l-tyrosine (3-NT), an important marker for oxidative stress, the level of which in our body signals several chronically diseased conditions. The enthalpy-driven interactions of CdSe/ZnS-GSH QDs with 3-NT were characterized through steady-state and time-resolved luminescence spectroscopy and isothermal microcalorimetry. The devised method of probing 3-NT was further validated with human serum samples. Thus, the proposed strategy may provide a protocol for selective determination of 3-NT under different pathological conditions.

In Situ Synthesis of a Bismuth Vanadate/Molybdenum Disulfide Composite: An Electrochemical Tool for 3-Nitro-l-Tyrosine Analysis

The quantification of 3-nitro-l-tyrosine (NO₂-Tyr), an in vivo biomarker of nitrosative stress, is indispensable for the clinical intervention of various inflammatory disorders caused by nitrosative stress. By integrating the unique features of BiVO₄ and MoS₂ with matching bandgap energies, electrode materials with amplified response signals can be developed. In this regard, we introduce a hydrothermally synthesized bismuth vanadate sheathed molybdenum disulfide (MoS₂@BiVO₄) heterojunction as a highly sensitive electrode material for the determination of NO₂-Tyr. Excellent electrochemical behavior perceived for the MoS₂@BiVO₄ augments the performance of the sensor and allows the measurement of NO₂-Tyr in biological media without any time-consuming pretreatments. The synergistic interactions between BiVO₄ and MoS₂ heterojunctions contribute to low resistance charge transfer (R_ct = 159.13 Ω·cm²), a reduction potential E_pc = -0.58 V (vs Ag/AgCl), and a good response range (0.001-526.3 μM) with a lower limit of detection (0.94 nM) toward the detection of NO₂-Tyr. An improved active surface area, reduced charge recombination, and high analyte adsorption contribute to the high loading of the biomarker for improved selectivity (in the presence of 10 interfering compounds), operational stability (1000 s), and reproducibility (six various modified electrodes). The proposed sensor was successfully utilized for the real-time determination of NO₂-Tyr in water, urine, and saliva samples with good recovery values (±98.94-99.98%), ascertaining the reliability of the method. It is noteworthy that the electrochemical activity remains unaffected by other redox interferons, thus leading to targeted sensing applications.

Ribonucleotide reductase: Implications of thiol S-nitrosylation and tyrosine nitration for different subunits

Ribonucleotide reductase (RNR) is a multi-subunit enzyme responsible for catalyzing the rate-limiting step in the production of deoxyribonucleotides essential for DNA synthesis and repair. The active RNR complex is composed of multimeric R1 and R2 subunits. The RNR catalysis involves the formation of tyrosyl radicals in R2 subunits and thiyl radicals in R1 subunits. Despite the quaternary structure and cofactor diversity, all the three classes of RNR have a conserved cysteine residue at the active site which is converted into a thiyl radical that initiates the substrate turnover, suggesting that the catalytic mechanism is somewhat similar for all three classes of the RNR enzyme. Increased RNR activity has been associated with malignant transformation, cancer cell growth, and tumorigenesis. Efforts concerning the understanding of RNR inhibition in designing potent RNR inhibitors/drugs as well as developing novel approaches for antibacterial, antiviral treatments, and cancer therapeutics with improved radiosensitization have been made in clinical research. This review highlights the precise and potent roles of NO in RNR inhibition by targeting both the subunits. Under nitrosative stress, the thiols of the R1 subunits have been found to be modified by S-nitrosylation and the tyrosyl radicals of the R2 subunits have been modified by nitration. In view of the recent advances and progresses in the field of nitrosative modifications and its fundamental role in signaling with implications in health and diseases, the present article focuses on the regulations of RNR activity by S-nitrosylation of thiols (R1 subunits) and nitration of tyrosyl residues (R2 subunits) which will further help in designing new drugs and therapies.

A highly selective and sensitive spectrofluorimetric method for the assessment of 3-nitrotyrosine in serum using (Eu(TTA)3Phen) photo probe

A simple, accurate and fast method was developed for the assessment of 3-nitrotyrosine as a biomarker for the early diagnosis of liver cirrhosis with minimal hepatic encephalopathy (MHE) using a (Eu(TTA)₃Phen) photo probe. 3-Nitrotyrosine can remarkably quench the luminescence intensity of the (Eu(TTA)₃Phen) complex in DMSO at pH = 9 and λ_em = 617 nm. The quenching of the luminescence intensity of (Eu(TTA)₃Phen) complex particularly the electrical emission band at λ_em = 617 nm is used for the assessment of 3-nitrotyrosine in different serum samples of patients with liver cirrhosis.

A simple, accurate and fast method was developed for the assessment of 3-nitrotyrosine as a biomarker for the early diagnosis of liver cirrhosis with minimal hepatic encephalopathy (MHE) using a (Eu(TTA)₃Phen) photo probe.

A chemiluminescence probe enhanced by cobalt and nitrogen-doped carbon dots for the determination of a nitrosative stress biomarker

A chemiluminometric method is introduced for the determination of the stress biomarker, 3-nitrotyrosine (3-NT) based on the H₂O₂-NaIO₄ reaction enhanced by cobalt and nitrogen-doped carbon dots (Co,N-CDs). In this chemiluminescence (CL) system, the emission proved to be originated from the excited-state Co,N-CDs (λ_max = 504 nm). Comparing the effect of Co,N-CDs with that of some other metal ion-doped CDs and undoped CDs indicated the high efficiency of Co,N-CDs in the CL amplification (about 1980-fold). This was attributed to the fact that Co,N-CDs, in addition to other functions, could act as catalytic center, to accelerate the decomposition of H₂O₂ and to increase the number of hydroxyl radicals. It was found that 3-NT inhibits the action of Co,N-CDs by an electron transfer process, leading to a decline in the CL intensity of the system. Therefore, a new CL sensing platform was introduced for the assay of 3-NT in the range 5.0 to 300 nM with a detection limit of 1.5 nM. The probe was utilized for the analysis of biological samples.

Real time detection of 3-nitrotyrosine using smartphone-based electrochemiluminescence

As an oxidase stress biomarker, 3-nitrotyrosine is closely associated with many cardiovascular diseases. Thus, early diagnosis and real time detection of 3-nitrotyrosine at bedside are highly important. Herein, we developed a handheld electrochemiluminescence (ECL) analysis device, which integrates printed circuit board (PCB) for electrical stimulation and smartphone for optical signals readout. Fast and accurate determination of 3-nitrotyrosine was achieved with Antibody/Ru(dcpy)₃²⁺@AuNPs/MoS₂ modified Au electrode (Ab/Ru@AuNPs/MoS₂) for ECL analysis. The linear range of 3-nitrotyrosine detection was from 10^-8 mol/L to 10^-6 mol/L with a detection limit of 8.4 × 10^-9 mol/L. In addition, an Android application was developed to realize real time analysis of ECL emissions and results readout for detection. To confirm the usage of the device, spiked serum with different concentrations was tested and the results indicated the practical reliability and stability of this device. The operating procedure for ECL analysis in this device is extremely easy and electrical stimulation was adjustable from 0 V to 5 V for general ECL systems. Thus, we believe this handheld device for ECL analysis has extensive prospects for application in Point-of-care testing and health caring.

Two-Step Derivatization of Amino Acids for Stable-Isotope Dilution GC-MS Analysis: Long-Term Stability of Methyl Ester-Pentafluoropropionic Derivatives in Toluene Extracts

Analysis of amino acids by gas chromatography-mass spectrometry (GC–MS) requires at least one derivatization step to enable solubility in GC–MS-compatible water-immiscible organic solvents such as toluene, to make them volatile to introduce into the gas chromatograph and thermally stable enough for separation in the GC column and introduction into the ion-source, and finally to increase their ionization by increasing their electronegativity using F-rich reagents. In this work we investigated the long-term stability of the methyl esters pentafluoropropionic (Me-PFP) derivatives of 21 urinary amino acids prepared by a two-step derivatization procedure and extraction by toluene. In situ prepared trideuteromethyl ester pentafluoropropionic derivatives were used as internal standards. GC–MS analysis (injection of 1 µL aliquots and quantification by selected-ion monitoring of specific mass fragments) was performed on days 1, 2, 8, and 15. Measured peak areas and calculated peak area ratios were used to evaluate the stability of the derivatives of endogenous amino acids and their internal standards, as well as the precision and the accuracy of the method. All analyses were performed under routine conditions. Me-PFP derivatives of endogenous amino acids and their stable-isotope labelled analogs were stable in toluene for 14 days. The peak area values of the derivatives of most amino acids and their internal standards were slightly higher on days 8 and 15 compared to days 1 and 2, yet the peak area ratio values of endogenous amino acids to their internal standards did not change. Our study indicates that Me-PFP derivatives of amino acids from human urine samples can easily be prepared, are stable at least for 14 days in the extraction solvent toluene, and allow for precise and accurate quantitative measurements by GC–MS using in situ prepared deuterium-labelled methyl ester as internal standard.

Simultaneous LC-MS/MS-Based Quantification of Free 3-Nitro-l-tyrosine, 3-Chloro-l-tyrosine, and 3-Bromo-l-tyrosine in Plasma of Colorectal Cancer Patients during Early Postoperative Period

Quantification with satisfactory specificity and sensitivity of free 3-Nitro-l-tyrosine (3-NT), 3-Chloro-l-tyrosine (3-CT), and 3-Bromo-l-tyrosine (3-BT) in biological samples as potential inflammation, oxidative stress, and cancer biomarkers is analytically challenging. We aimed at developing a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based method for their simultaneous analysis without an extract purification step by solid-phase extraction. Validation of the developed method yielded the following limits of detection (LOD) and quantification (LOQ) for 3-NT, 3-BT, and 3-CT: 0.030, 0.026, 0.030 ng/mL (LODs) and 0.100, 0.096, 0.098 ng/mL (LOQs). Coefficients of variation for all metabolites and tested concentrations were <10% and accuracy was within 95-105%. Method applicability was tested on colorectal cancer patients during the perioperative period. All metabolites were significantly higher in cancer patients than healthy controls. The 3-NT was significantly lower in advanced cancer and 3-BT showed a similar tendency. Dynamics of 3-BT in the early postoperative period were affected by type of surgery and presence of surgical site infections. In conclusion, a sensitive and specific LC-MS/MS method for simultaneous quantification of free 3-NT, 3-BT, and 3-CT in human plasma has been developed.

Detection and quantification of nitric oxide-derived oxidants in biological systems

The free radical nitric oxide (NO^•) exerts biological effects through the direct and reversible interaction with specific targets (e.g. soluble guanylate cyclase) or through the generation of secondary species, many of which can oxidize, nitrosate or nitrate biomolecules. The NO^•-derived reactive species are typically short-lived, and their preferential fates depend on kinetic and compartmentalization aspects. Their detection and quantification are technically challenging. In general, the strategies employed are based either on the detection of relatively stable end products or on the use of synthetic probes, and they are not always selective for a particular species. In this study, we describe the biologically relevant characteristics of the reactive species formed downstream from NO^•, and we discuss the approaches currently available for the analysis of NO^•, nitrogen dioxide (NO₂ ^•), dinitrogen trioxide (N₂O₃), nitroxyl (HNO), and peroxynitrite (ONOO^-/ONOOH), as well as peroxynitrite-derived hydroxyl (HO^•) and carbonate anion (CO₃ ^•-) radicals. We also discuss the biological origins of and analytical tools for detecting nitrite (NO₂ ^-), nitrate (NO₃ ^-), nitrosyl-metal complexes, S-nitrosothiols, and 3-nitrotyrosine. Moreover, we highlight state-of-the-art methods, alert readers to caveats of widely used techniques, and encourage retirement of approaches that have been supplanted by more reliable and selective tools for detecting and measuring NO^•-derived oxidants. We emphasize that the use of appropriate analytical methods needs to be strongly grounded in a chemical and biochemical understanding of the species and mechanistic pathways involved.

A novel analytical method based on HPLC-PDA coupled post-column derivatization to evaluate the ability to inhibit tyrosine nitration in lotus leaf extracts

Protein tyrosine nitration plays a key role in many inflammatory and cardiovascular diseases and diabetes. Many natural products are used to treat these diseases through their ability to potentially interfere this reaction. Here, we describe a novel method to provide active fingerprinting of inhibition of tyrosine nitration by natural products based on post-column tyrosine nitration reaction analysis using high-performance liquid chromatography coupled to a photometric diode array. Results indicated that lotus leaf extracts exhibited obvious inhibitory activity against tyrosine nitration by peroxynitrite, and that chemical and active fingerprints were simultaneously established, with the active fingerprints indicating the active compounds of the lotus leaves. Additionally, flavonoids were screened as the principal active compounds involved in inhibiting tyrosine nitration in the lotus leaf extracts, with quercetin-3-O-glucuronide and quercetin-3-O-glucoside exhibiting the greatest contributions. Moreover, our results suggested that lotus leaves from three regions (Nanjing, Suzhou, and Hangzhou) exhibited the best inhibitory activity. These findings indicated the usefulness of this method for screening active compounds involved in inhibiting protein tyrosine nitration, and that similar strategies can likely be applied to evaluate the inhibitory activity against tyrosine nitration of other natural products.

A novel analytical method based on HPLC-PDA coupled post-column derivatization to evaluate the inhibitory activity of tyrosine nitration in lotus leaf extracts.

Integration of Miniaturized Solid Phase Extraction and LC-MS/MS Detection of 3-Nitrotyrosine in Human Urine for Clinical Applications

Free 3-nitrotyrosine (3-NT) has been extensively used as a possible biomarker for oxidative stress. Increased levels of 3-NT have been reported in a wide variety of pathological conditions. However, existing methods lack the sufficient sensitivity and/or specificity necessary to measure the low endogenous level of 3-NT reliably and are too cumbersome for clinical applications. Hence, analytical improvement is urgently needed to accurately quantify the levels of 3-NT and verify the role of 3-NT in pathological conditions. This protocol presents the development of a novel liquid chromatography tandem mass spectrometry (LC-MS/MS) detection combined with a miniaturized solid phase extraction (SPE) for the rapid and accurate measurement of 3-NT in human urine as a non-invasive biomarker for oxidative stress. SPE using a 96-well plate markedly simplified the process by combining sample cleanup and analyte enrichment without tedious derivatization and evaporation steps, reducing solvent consumption, waste disposal, risk of contamination and overall processing time. The employment of 25 mM ammonium acetate (NH4OAc) at pH 9 as the SPE elution solution substantially enhanced the selectivity. Mass spectrometry signal response was improved through adjustment of the multiple reaction monitoring (MRM) transitions. Use of 0.01% HCOOH as additive on a pentafluorophenyl (PFP) column (150 mm x 2.1 mm, 3 µm) improved signal response another 2.5-fold and shortened the overall run time to 7 min. A lower limit of quantitation (LLOQ) of 10 pg/mL (0.044 nM) was achieved, representing a significant sensitivity improvement over the reported assays. This simplified, rapid, selective and sensitive method allows two plates of urine samples (n = 192) to be processed in a 24 h time-period. Considering the markedly improved analytical performance, and non-invasive and inexpensive urine sampling, the proposed assay is beneficial for pre-clinical and clinical studies.

Bioorthogonal labelling of 3-nitrotyrosine in peptides and proteins through diazotisation mediated azidation

A bioorthogonal method of transforming 3-nitrotyrosine to 3-azidotyrosine is described, providing new opportunities to study 3-nitrotyrosine in biological samples.

Multimarker screening of oxidative stress in aging

Aging is a complex process of organism decline in physiological functions. There is no clear theory explaining this phenomenon, but the most accepted one is the oxidative stress theory of aging. Biomarkers of oxidative stress, substances, which are formed during oxidative damage of phospholipids, proteins, and nucleic acids, are present in body fluids of diseased people as well as the healthy ones (in a physiological concentration). 8-iso prostaglandin F_2α is the most prominent biomarker of phospholipid oxidative damage, o-tyrosine, 3-chlorotyrosine, and 3-nitrotyrosine are biomarkers of protein oxidative damage, and 8-hydroxy-2^′-deoxyguanosine and 8-hydroxyguanosine are biomarkers of oxidative damage of nucleic acids. It is thought that the concentration of biomarkers increases as the age of people increases. However, the concentration of biomarkers in body fluids is very low and, therefore, it is necessary to use a sensitive analytical method. A combination of HPLC and MS was chosen to determine biomarker concentration in three groups of healthy people of a different age (twenty, forty, and sixty years) in order to find a difference among the groups.

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.

Good mass spectrometry and its place in good science

The mass spectrometry community has expanded as instruments became more powerful, user-friendly, affordable and readily available. This opens up opportunities for novice users to perform high impact research, using highly advanced instrumentation. This introductory tutorial is targeted at the novice user working in a research setting. It aims to offer the benefit of other people's experiences and to help newcomers avoid known pitfalls and problematic issues. It discusses some of the essential features of sound analytical chemistry and highlights the need to use validated analytical methods that provide high quality results along with a measure of their uncertainty. Examples are used to illustrate potential pitfalls and their consequences.

Measurement of 3-nitro-tyrosine in human plasma and urine by gas chromatography-tandem mass spectrometry

Reaction of reactive nitrogen species (RNS), such as peroxynitrite and nitryl chloride with soluble tyrosine and tyrosine residues in proteins produces soluble 3-nitro-tyrosine and 3-nitro-tyrosino-proteins, respectively. Regular proteolysis of 3-nitro-tyrosino-proteins yields soluble 3-nitro-tyrosine. 3-Nitro-tyrosine circulates in plasma and is excreted in the urine. Both circulating and excretory 3-nitro-tyrosine are considered suitable biomarkers of nitrative stress. Tandem mass spectrometry coupled with gas chromatography (GC-MS/MS) or liquid chromatography (LC-MS/MS) is one of the most reliable analytical techniques to determine 3-nitro-tyrosine. Here, we describe protocols for the quantitative determination of soluble 3-nitro-tyrosine in human plasma and urine by GC-MS/MS.

Unique pentafluorobenzylation and collision-induced dissociation for specific and accurate GC-MS/MS quantification of the catecholamine metabolite 3,4-dihydroxyphenylglycol (DHPG) in human urine

In the human body, the catecholamine norepinephrine is mainly metabolized to 3,4-dihydroxyphenylglycol (DHPG) which therefore serves as an important biomarker for norepinephrine's metabolism. Most data on DHPG concentrations in human plasma and urine has been generated by using HPLC-ECD or GC-MS technologies. Here, we describe a stable-isotope dilution GC-MS/MS method for the quantitative determination of DHPG in human urine using trideutero-DHPG (d(3)-DHPG) as internal standard and a two-step derivatization process with pentafluorobenzyl bromide (PFB-Br) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). Two pentafluorobenzyl (PFB) trimethylsilyl (TMS) derivatives were obtained and identified, i.e., two isomeric DHPG-PFB-(TMS)(3) derivatives and the later eluting DHPG-tetrafluorobenzyl-(TMS)(2) derivative, i.e., DHPG-TFB-(TMS)(2). To our knowledge the DHPG-TFB-(TMS)(2) derivative and the underlying reaction have not been reported previously. In this reaction both vicinal aromatic hydroxyl groups of DHPG react with PFB-Br to form a heterocyclic seven-membered [1,4]dioxepin compound. The DHPG-TFB-(TMS)(2) derivative was used for quantitative GC-MS/MS analysis in the electron-capturing negative-ion chemical ionization mode by selected-reaction monitoring of m/z 351 from m/z 401 for DHPG and of m/z 352 from m/z 404 for d(3)-DHPG. Validation experiments on human urine samples spiked with DHPG in a narrow (0-33 nM) and a wide range (0-901 nM) revealed high recovery (86-104%) and low imprecision (RSD; 0.01-2.8%). LOD and relative LLOQ (rLLOQ) values of the method for DHPG were determined to be 76 amol and 9.4%, respectively. In urine of 28 patients suffering from chronic inflammatory rheumatic diseases, DHPG was measured at a mean concentration of 238 nM (38.3 μg/g creatinine). The DHPG concentration in the respective control group of 40 healthy subjects was measured to be 328 nM (39.2 μg/g creatinine). Given the unique derivatization reaction and collision-induced dissociation, and the straightforwardness the present method is highly specific, accurate, precise, and should be useful in clinical settings.

Rapeseed protein in a high-fat mixed meal alleviates postprandial systemic and vascular oxidative stress and prevents vascular endothelial dysfunction in healthy rats

High-saturated fat and high-sucrose meals induce vascular endothelial dysfunction, the early hallmark of atherogenesis. The impact of dietary protein on vascular homeostasis remains misunderstood. In this study, we investigated whether rapeseed protein, an emergent arginine- and cysteine-rich protein, can acutely modulate the onset of adverse effects induced by a high-saturated fat meal (HFM). In a series of crossover experiments, healthy rats received 3 HFM (saturated fat: 60%; sucrose: 20%; protein: 20% energy) with the protein source being either total milk protein (MP; control), rapeseed protein (RP), or MP supplemented with cysteine and arginine to the same level as in RP (MP+AA). Endothelium-related vascular reactivity, measured as an acetylcholine-induced transient decrease in blood pressure, and plasma triglycerides, hydroperoxides, cyclic GMP (cGMP), and free 3-nitrotyrosine were measured before and 2, 4, and 6 h after meals. Superoxide anion production, expressed as ethidine fluorescence, was measured in the aorta 6 h after meals. Whereas plasma triglycerides rose similarly in all meals, the decrease in vascular reactivity after MP was attenuated after MP+AA and entirely prevented after RP. The type of meal had no consistent effect on plasma cGMP and free 3-nitrotyrosine over the postprandial period. The postprandial increase in plasma hydroperoxides differed according to the meal, and concentrations were 43% lower 6 h after MP+AA and RP than after MP. Aortic superoxide anion production was 36% lower 6 h after RP than MP. These results show that substituting rapeseed protein for milk protein markedly reduces vascular and oxidative disturbances induced by an HFM and this may be mediated in part by cysteine and arginine.

Nitrotyrosine promotes human aortic smooth muscle cell migration through oxidative stress and ERK1/2 activation

Nitrotyrosine is a new biomarker of atherosclerosis and inflammation. The objective of this study was to determine the direct effects of free nitrotyrosine on human aortic smooth muscle cell (AoSMC) migration and molecular mechanisms. By a modified Boyden chamber assay, nitrotyrosine significantly increased AoSMC migration in a concentration-dependent manner. For example, nitrotyrosine at 300 nM increased AoSMC migration up to 152% compared with l-tyrosine-treated control cells (P<0.01). Cell wound healing assay confirmed this effect. Nitrotyrosine significantly increased the expression of some key cell migration-related molecules including PDGF receptor-B, matrix metalloproteinase 2 (MMP2) and integrins alphaV and beta3 at both mRNA and protein levels in AoSMC (P<0.01). In addition, nitrotyrosine increased reactive oxygen species (ROS) production in AoSMC by staining with fluorescent dye DCFHDA. Furthermore, nitrotyrosine induced transient phosphorylation of ERK2 by Bio-Plex luminex immunoassay and western blot analysis. AoSMC were able to uptake nitrotyrosine. Antioxidants including seleno-l-methionine and superoxide dismutase mimetic (MnTBAP) as well as ERK1/2 inhibitor PD98059 effectively blocked the promoting effect of nitrotyrosine on AoSMC migration and the mRNA expression of above cell migration-related molecules. Thus, nitrotyrosine directly increases AoSMC migration in vitro and the expression of migration-related molecules through overproduction of ROS and activation of ERK1/2 pathway. Nitrotyrosine may contribute to cardiovascular pathogenesis.

Nitration of soluble proteins in organotypic culture models of Parkinson's disease

Protein nitration due to oxidative and nitrative stress has been linked to the pathogenesis of Parkinson's disease (PD), but its relationship to the loss of dopamine (DA) or tyrosine hydroxylase (TH) activity is not clear. Here we quantified protein-bound 3-nitrotyrosine (3-NT) by a novel gas chromatography/negative chemical ionization tandem mass spectrometry technique and DA and 3,4-dihydroxyphenylalanine (DOPA) by HPLC in tissues or medium of organotypic, mouse mesencephalon cultures after acute or chronic treatments with the peroxynitrite donor 3-morpholino-sydnonimine (SIN-1), the dopaminergic toxin 1-methyl-4-phenylpyridinium (MPP(+)) or the lipophilic complex I inhibitor rotenone. Incubation with SIN-1 (24 h) or MPP(+) treatments (48 h) caused dose-dependent protein nitration reaching a maximum of eightfold increase by 10 mM SIN-1 or twofold by 10 microM MPP(+), but significant DA depletions occurred at much lower concentrations of MPP(+) (1 microM). Chronic MPP(+) or rotenone treatments (3 weeks) caused maximum protein nitration by 1 microM (twofold) or 10nM (fourfold), respectively. Co-treatment with the nitric oxide synthase inhibitor l-NAME (300 microM) prevented protein nitration by MPP(+), but did not protect against MPP(+)-induced DA depletion or inhibition of TH activity. Acute incubation with 100 microM SIN-1 inhibited TH activity, which could be blocked by co-treatment with the tetrahydrobiopterin precursor l-sepiapterin, but tissue DA depletions required higher doses of SIN-1 (>1 mM, 24 h) and longer survival. In conclusion, protein nitration and TH activity or DA depletion are not directly related in these models.

Assay of 3-nitrotyrosine in tissues and body fluids by liquid chromatography with tandem mass spectrometric detection

3-Nitrotyrosine (3-NT) is a marker of protein nitration in physiological systems. It is present as 3-nitrotyrosine residues in proteins of tissue, extracellular matrix, plasma, and other body fluids and food. It is also present in body fluids and some beverages as free nitrotyrosine and is excreted in urine with the major urinary metabolite 3-nitro-4-hydroxyphenylacetic acid. Quantitation of 3-nitrotyrosine requires tandem mass spectrometry for specific detection. The method developed to determine 3-nitrotyrosine (along with protein glycation and oxidation adducts in a quantitative screening assay) by liquid chromatography with tandem mass spectrometric detection is described. The 3-NT residue contents of plasma protein, hemoglobin, lipoproteins, and cerebrospinal fluid protein and the concentrations of free 3-nitrotyrosine in plasma, urine, and cerebrospinal fluid are given. Changes of 3-nitrotyrosine residue and free 3-nitrotyrosine in diabetes, cirrhosis, acute and chronic renal failure, and neurological disorders, including Alzheimer's disease, are presented and compared with independent estimates.

Protein 3-nitrotyrosine in complex biological samples: quantification by high-pressure liquid chromatography/electrochemical detection and emergence of proteomic approaches for unbiased identification of modification sites

Nitration of tyrosine residues by nitric oxide (NO)-derived species results in the accumulation of 3-nitrotyrosine in proteins, a hallmark of nitrosative stress in cells and tissues. Tyrosine nitration is recognized as one of the multiple signaling modalities used by NO-derived species for the regulation of protein structure and function in health and disease. Various methods have been described for the quantification of protein 3-nitrotyrosine residues, and several strategies have been presented toward the goal of proteome-wide identification of protein tyrosine modification sites. This chapter details a useful protocol for the quantification of 3-nitrotyrosine in cells and tissues using high-pressure liquid chromatography with electrochemical detection. Additionally, this chapter describes a novel biotin-tagging strategy for specific enrichment of 3-nitrotyrosine-containing peptides. Application of this strategy, in conjunction with high-throughput MS/MS-based peptide sequencing, is anticipated to fuel efforts in developing comprehensive inventories of nitrosative stress-induced protein-tyrosine modification sites in cells and tissues.

Chromatographic and mass spectrometric methods for quantitative determination of 3-nitrotyrosine in biological samples and their application to human samples

The permanent modification of soluble and protein-associated tyrosine by nitration results in the formation of 3-nitrotyrosine, which can be used as a marker of "nitro-oxidative" damage to proteins. Based on the analysis of patient materials, over 40 different diseases and/or conditions have been linked to increased nitration of tyrosine. They include many cardiovascular diseases, conditions associated with immunological reactions and neurological diseases. In this article we review the existing chromatographic and mass spectrometric methods for quantitative measurements of 3-nitrotyrosine in different human biological samples including plasma, either from the free amino acid pool or from hydrolyzed proteins from different matrices.

A comparative study of proteolysis methods for the measurement of 3-nitrotyrosine residues: enzymatic digestion versus hydrochloric acid-mediated hydrolysis

A common approach for the quantification of 3-nitrotyrosine (NY) in routine analyses relies on the cleavage of peptide bonds in order to release the free amino acids from proteins in tissues or fluids. NY is usually monitored by either GC-MS(/MS) or LC-MS/MS techniques. Various proteolysis methods have been employed to combine digestion efficiency with prevention of artifactual nitration of tyrosine. However, so far, no study was designed to compare the HCl-based hydrolysis method with enzymatic digestion in terms of reliability for the measurement of NY. The present work addresses the digestion efficiency of BSA using either 6M HCl, pronase E or a cocktail of enzymes (pepsin, pronase E, aminopeptidase, prolidase) developed in our laboratory. The HCl-based hydrolysis leads to a digestion yield of 95%, while 25 and 75% are achieved with pronase E and the cocktail of enzymes, respectively. These methods were compared in terms of NY measurement and the results indicate that a prior reduction of the disulfide bonds ensures a reliable quantification of NY. We additionally show that the enzyme efficacy is not altered when the digestion is carried out in the presence of BSA with a high content of NY.

Determination of nitrotyrosine and tyrosine by high-performance liquid chromatography with tandem mass spectrometry and immunohistochemical analysis in livers of mice administered acetaminophen

Nitrotyrosine (NTYR) is used as a biomarker of nitrative pathology caused by peroxynitrite (ONOO-) formation. NTYR measurement in biological materials usually employs such methodologies as immunohistochemistry staining, high-performance liquid chromatography and gas chromatography. In this study, we developed a method for the determination of tyrosine (TYR) and NTYR, using liquid chromatography with tandem mass spectrometry (LC-MS/MS). In order to confirm the applicability of our method to an in vivo system, we measured protein-bound NTYR levels using by LC-MS/MS method and immunohistochemical analysis in liver of B6C3F1 mice at 2 h, 4 h and 8 h after administration of 300 mg/kg acetaminophen (APAP). A mass spectrometer equipped with an electrospray ionization source using a crossflow counter electrode and ran in the positive ion mode (ESI+) was set up for multiple reaction monitoring (MRM), which monitored the transitions 182.2>136.2, 227.1>181.2, 191.3>144.4 and 236.3>189.5, for TYR, NTYR, [13C9]-TYR and [13C9]-NTYR, respectively. The average recoveries from mice liver protein samples spiked with 25 microM TYR and 100 nM NTYR were 94.4% and 95.6%, respectively, with correction using the added surrogate standards. The limits of quantification were 100 nM for TYR and 0.5 nM for NTYR. NTYR was detected all liver samples of mice by the proposed LC-MS/MS method. The concentration range of NTYR per milligram protein in samples was 0.17-0.3 pmol/mg protein. And the level reached a maximum at 4 h. These data were well correlated with the result obtained by an immunohistochemical reaction with anti-NTYR antibody. The LC-MS/MS method was able to determine protein-bound NTYR in a small amount of tissue sample, and is therefore expected to be a very powerful tool for evaluating ONOO- generation in an in vivo system.

Biomarkers of oxidative damage in human disease

Oxidative/nitrosative stress, a pervasive condition of increased amounts of reactive oxygen/nitrogen species, is now recognized to be a prominent feature of many acute and chronic diseases and even of the normal aging process. However, definitive evidence for this association has often been lacking because of recognized shortcomings with biomarkers and/or methods available to assess oxidative stress status in humans. Emphasis is now being placed on biomarkers of oxidative stress, which are objectively measured and evaluated as indicators of normal biological processes, pathogenic processes, or pharmacologic responses to therapeutic intervention. To be a predictor of disease, a biomarker must be validated. Validation criteria include intrinsic qualities such as specificity, sensitivity, degree of inter- and intraindividual variability, and knowledge of the confounding and modifying factors. In addition, characteristics of the sampling and analytical procedures are of relevance, including constraints and noninvasiveness of sampling, stability of potential biomarkers, and the simplicity, sensitivity, specificity, and speed of the analytical method. Here we discuss some of the more commonly used biomarkers of oxidative/nitrosative damage and include selected examples of human studies.

Quantification of 3-nitrotyrosine levels using a benchtop ion trap mass spectrometry method

Oxidative damage by reactive nitrogen species is linked to the pathogenesis of numerous inflammatory disorders, including atherosclerosis. 3-Nitrotyrosine (NO2Tyr), a posttranslational modification of proteins generated by reactive nitrogen species, serves as a "molecular fingerprint" for protein modification by nitric oxide (NO)-derived oxidants. Studies demonstrate that systemic levels of protein-bound NO2Tyr serve as an independent predictor of cardiovascular risks and are modulated by statin therapy. Measurement of NO2Tyr in biological matrices may thus serve both as a quantitative index of nitrative stress in vivo and an important new prognostic marker of clinical relevance. Analytical methods for the accurate detection and quantification of trace levels of NO2Tyr in biological tissues and fluids are, thus, of considerable interest. Here, we describe a rapid, sensitive, and specific method for the quantification of NO2Tyr in biological matrices using readily available benchtop ion-trap mass spectrometry instrumentation (e.g., LCQDeca) combined with high-performance liquid chromatography (HPLC) interface. Through judicious use of stable isotopically labeled precursors as synthetic internal standards, the tandem mass spectrometric method described simultaneously adjusts for potential intrapreparative sample losses and monitors potential artifactual generation of NO2Tyr during processing. The described method permits rapid and reproducible quantification of NO2Tyr in biological and clinical specimens at the 100 fmol on column detection limit and should prove useful for studies defining the impact of reactive nitrogen species in cardiovascular disease and other inflammatory disorders.

Selective quantification of free 3-nitrotyrosine in exhaled breath condensate in asthma using gas chromatography/tandem mass spectrometry

Reactive nitrogen species can cause oxidative modifications of certain amino acid residues in proteins, notably the modification of tyrosine to 3-nitrotyrosine (3-NT), which is a potentially useful marker of oxidative stress. Since lung diseases are associated with airway inflammation and oxidative stress, quantification of 3-NT in exhaled breath condensate (EBC) may provide a non-invasive means for monitoring ongoing inflammatory processes. 3-NT-like immunoreactivity has previously been detected in EBC, but no definitive evidence for the presence of 3-NT in EBC is available. Here, a method based on gas chromatography/negative ion chemical ionization/tandem mass spectrometry was established for the quantification of free 3-NT in EBC. The detection limit was 0.56 pM (corresponding to 3.0 amol microl(-1) sample injected) and the method was found to give linear results (r2 > 0.999) in the concentration range of 0-5.0 nM. The coefficient of variation (CV) for within-day and between-day precision were 11 and 12%, respectively. No artifactual nitration was observed during sample processing. The method was applied to study subjects with asthma (n = 8), and healthy subjects (n = 10), but only a slight non-significant increase in 3-NT levels was found in the former group (median [interquartile ranges]; 99 [50-547] amol s(-1) vs. 75 [35-147] amol s(-1)). No correlation with exhaled nitric oxide (NO), pulmonary function or EBC levels of total protein was observed. The 3-NT levels were much lower compared to previously reported levels, based on immunochemical measurements. The method does not allow the simultaneous quantification of tyrosine in samples.

Trace analysis of oxidized, nitrated, and chlorinated aromatic amino acids by capillary electrophoresis with electroosmotic flow modification allowing large-volume sample stacking

A capillary electrophoresis method has been developed for the simultaneous analysis of the oxidized, nitrated, and chlorinated aromatic amino acids, as well as their parent compounds. These modifications of the aromatic amino acids in proteins or free form are induced by the attack of reactive, mainly free radical species generated during cell stress, and these stable products may serve as biomarkers of cell damage. The analytes tyrosine, phenylalanine, dihydroxyphenylalanine, tryptophan, 3-nitrotyrosine, 3-chlorotyrosine, ortho-tyrosine, meta-tyrosine, 3-hydroxyphenylacetic acid (internal standard 1), and alpha-methyltyrosine (internal standard 2) were separated in their anionic forms in alkaline borate buffer. The polyamine spermine was used as electroosmotic flow (EOF) modifier. Adsorbing to the capillary wall, spermine can either suppress or even reverse the EOF depending on its concentration and the pH. The effects of the pH of the separation buffer, the spermine concentration, the temperature, and the applied field strength on the separation were examined. The modified aromatic amino acids are present in biological fluids in a much lower concentration than their parent compounds, thus high detection sensitivity of the analytical method is required. To achieve good detection sensitivity, field-amplified sample stacking of large injection volumes was applied. Omitting polyamine from the sample buffer allowed local reversal of the EOF, thus removal of the low conductivity sample buffer at the capillary inlet. In this way, 100% of the capillary to the detection window could be filled with the sample, and the detection limits achieved for the modified aromatic amino acids were in the range of 2.5-10 nM.

Recent methodological advances in the mass spectrometric analysis of free and protein-associated 3-nitrotyrosine in human plasma

L-Tyrosine and L-tyrosine residues in proteins are attacked by various reactive-nitrogen species (RNS) including peroxynitrite to form 3-nitrotyrosine (NO(2)Tyr) and protein-associated 3-nitrotyrosine (NO(2)TyrProt). Circulating NO(2)Tyr and NO(2)TyrProt have been suggested and are widely used as biomarkers of oxidative stress in humans. In this article the mass spectrometry (MS)-based analytical methods recently reported for the quantification of circulating levels of NO(2)Tyr and NO(2)TyrProt are discussed. These methodologies differ in sensitivity, selectivity, specificity and accessibility to interferences with the latter mainly arising from artifactual formation of NO(2)Tyr and NO(2)TyrProt during sample treatment such as acidification and chemical derivatization. Application of these methodologies to healthy normal humans revealed basal circulating levels for NO(2)Tyr which range between 0.7 and 64 nM, i.e. by two orders of magnitude. Application of gas chromatography-tandem mass spectrometry (GC-tandem MS) methods by two independent research groups by using two different protocols to avoid artifactual nitration of L-tyrosine revealed almost identical mean plasma levels of the order of 1.0 nM in healthy humans. The lower limits of quantitation (LOQ) of these methods were 0.125 and 0.3n M, respectively. This order of magnitude for basal NO(2)Tyr is supported by two liquid chromatography-tandem mass spectrometry (LC-tandem MS) methods with LOQ values of 4.4 and 1.4 nM. On the basis of the data provided by GC-tandem MS and LC-tandem MS the use of a range of 0.5-3 nM for NO(2)Tyr and of 0.6 pmol/mg plasma protein or a molar ratio of 3-nitrotyrosine to tyrosine in plasma proteins of the order of 1:10(6) for NO(2)TyrProt in plasma of healthy humans as reference values appear reasonably justified. Recently reported clinical studies involving 3-nitrotyrosine as a biomarker of oxidative stress are discussed in particular from the analytical point of view.