Nitrotyrosine in plasma of celiac disease patients as detected by a new sandwich ELISA

Effects of angiotensin converting enzyme inhibitor and angiotensin II receptor antagonist combination on nitric oxide bioavailability and atherosclerotic change in Watanabe heritable hyperlipidemic rabbits

We investigated the effects of co-administration of an angiotensin-converting enzyme inhibitor (ACEI) and angiotensin type 1 receptor blocker (ARB) on nitric oxide (NO) bioavailability in genetically hyperlipidemic rabbits with our newly developed NO sensor. Plasma NO was measured using the new NO sensor in the abdominal aorta of anesthetized Watanabe heritable hyperlipidemic (WHHL) rabbits. Acetylcholine (ACh)-stimulated (20 microg in 5 min into the aortic arch) NO production was recorded after an 8 week per os pretreatment with 1) vehicle (control), 2) the ACEI enalapril (E: 3 mg/kg/day), 3) the ARB losartan (L: 30 mg/kg/day) and 4) enalapril (1.5 mg/kg/day)+losartan (15 mg/kg/day) (E+L). Intra-aortic infusion of ACh produced an increase in plasma NO concentration, which was significantly greater with all the drug treatments than with the control. E increased ACh-induced NO significantly more than L (by 6.9 nmol/L, and 4.7 nmol/L, respectively). E+L increased ACh-induced NO by 9.5 nmol/L, significantly more than either E or L. Plasma peroxynitrite concentration was 1.2 pmol/mg protein in the control group and significantly less than in the E- and L-group. The lowest peroxynitrite concentration was observed in the E+L group (0.5 pmol/mg protein), which was significantly lower than in the E-group and the L-group. Optical coherence tomography and histology of the thoracic aorta revealed that the plaque area decreased significantly more with the combination than with the monotherapy (p<0.01). In conclusion, the combined treatment with an ACEI and an ARB may have additive protective effects on endothelial function as well as atherosclerotic change.

Conversion of tyrosine to the inflammation-associated analog 3'-nitrotyrosine at either TCR- or MHC-contact positions can profoundly affect recognition of the MHC class I-restricted epitope of lymphocytic choriomeningitis virus glycoprotein 33 by CD8 T cells

Immunohistochemical detection of increased levels of protein-associated nitrotyrosine has become widely used as a surrogate marker of in situ inflammation. However, the potential consequences of protein-associated nitrotyrosine formation in terms of cellular immune recognition has received surprisingly little attention. Using a well-defined I-E(K)-restricted epitope of pigeon cytochrome c, we previously demonstrated that conversion of a single tyrosine residue to nitrotyrosine can have a profound effect on recognition by CD4 T cells. In this study, we used the MHC class I-restricted epitope of lymphocytic choriomeningitis virus glycoprotein (gp33) to demonstrate that conversion of tyrosine to nitrotyrosine can also profoundly affect recognition of MHC class I-restricted epitopes. Conversion of the Y4 residue of the gp33 epitope to nitrotyrosine completely abrogated recognition by gp33-specific T cells from P14 TCR-transgenic mice. In contrast, CD8(+) T cells specific for "nitrated gp33" (NY-gp33) can be readily elicited in C57BL/6 mice after immunization with NY-gp33 peptide. Interestingly, T-T hybridomas specific for NY-gp33 peptide were found to fall into two distinct subsets, being specific for NY-gp33 presented in the context of either H-2D(b) or H-2K(b). This latter result is surprising in light of previous structural studies showing that Y4 comprises a critical TCR-contact residue when presented by H-2D(b) but that the same residue points downward into the peptide-binding groove of the MHC when presented by H-2K(b). Together, these results indicate that nitrotyrosine formation can impact T cell recognition both directly, through alteration of TCR-contact residues, or indirectly, through alterations in MHC-contact positions.

Effect of pioglitazone on nitroglycerin-induced impairment of nitric oxide bioavailability by a catheter-type nitric oxide sensor

BACKGROUND

We examined whether nitroglycerin (NTG)-induced impairment of nitric oxide (NO) bioavailability could be modified by a peroxisome proliferator-activated receptor (PPAR) gammaagonist.

METHODS AND RESULTS

Male New Zealand White rabbits were treated for 7 days with NTG patches, either alone or in combination with pioglitazone. Plasma NO concentration was measured with the catheter-type NO sensor located in the aorta. N(G)-methyl-L-arginine and acetylcholine (ACh) were infused into the aortic arch to measure the basal and ACh-induced plasma NO concentrations. Vascular nitrotyrosine and tetrahydrobiopterin (BH(4)) concentrations were measured by enzyme-linked immunosorbent assay and high-performance liquid chromatography with fluorescence detection, respectively. The negative effects of NTG, that is, the decrease in basal and ACh-induced NO production, were significantly suppressed by co-treatment with pioglitazone. NTG-induced increases in vascular nitrotyrosine and BH(4) concentrations were significantly decreased with co-treatment with pioglitazone.

CONCLUSIONS

NTG-induced impairment of basal and ACh-stimulated NO production might be prevented by the co-treatment with a PPAR gamma agonist, pioglitazone through suppressions of nitrosative stress.

Analysis of oxidative modification of proteins

Protein oxidation has been implicated in a variety of degenerative diseases as well as in the aging process. This unit describes techniques for the quantification of various protein oxidation products, including protein carbonyls, loss of protein thiol groups, dityrosine and nitrotyrosine, and isoaspartate formation. Such oxidatively modified products may also be used as biomarkers for the assessment of oxidative stress during aging and/or disease.

Addition of eplerenone to an angiotensin-converting enzyme inhibitor effectively improves nitric oxide bioavailability

Angiotensin II and aldosterone both promote endothelial dysfunction and atherosclerosis. We investigated the effect of a combination of eplerenone, a selective aldosterone antagonist, and enalapril, an angiotensin-converting enzyme inhibitor, on NO bioavailability and spontaneous atherosclerotic changes. Twenty-four myocardial infarction-prone Watanabe heritable hyperlipidemic rabbits were treated with vehicle (control), eplerenone (50 mg/kg per day), enalapril (3 mg/kg per day), or eplerenone plus enalapril for 8 weeks (n=6 in each group). After treatment, acetylcholine-induced NO production was measured as a surrogate for endothelium-protective function, and vascular peroxynitrite (a product of superoxide and NO) was measured to assess dysfunctional endothelial NO synthase activity. Plaque area was quantified by histology. Intra-aortic infusion of acetylcholine produced an increase in plasma NO concentration that was significantly higher with all of the drug treatments compared with the control. Eplerenone and enalapril, in combination, increased acetylcholine-induced NO by 7.9 nM, which was significantly higher than with either eplerenone or enalapril alone. Vascular peroxynitrite was significantly higher in the control group (1.3 pmol/mg of protein) and significantly lower with combination treatment (0.4 pmol/mg of protein) compared with the enalapril or eplerenone group. The highest tetrahydrobiopterin levels were observed after cotreatment with eplerenone and enalapril. Histology of the thoracic aorta showed a significantly decreased plaque area with combination therapy compared with monotherapy. Combined treatment with a selective aldosterone antagonist and an angiotensin-converting enzyme inhibitor has additive protective effects on endothelial function and on atherosclerotic changes via decreased nitrosative stress.

Effects of pioglitazone on nitric oxide bioavailability measured using a catheter-type nitric oxide sensor in angiotensin II-infusion rabbit

Recently, peroxisome proliferator-activated receptor gamma (PPARgamma) ligands have been reported to increase nitric oxide (NO) bioavailability in vitro but not in vivo because of the difficulty of measuring plasma NO. Here, we investigated the effects of PPARgamma on plasma NO concentrations using the newly developed NO sensor in angiotensin II (Ang II)-infused rabbits. Male New Zealand rabbits were randomized for infusion with Ang II, either alone or in combination with pioglitazone (a PPARgamma agonist). Plasma NO concentration was measured using the catheter-type NO sensor placed in the aorta. We then infused N(G)-methyl-L-arginine (L-NMMA) and acetylcholine (ACh) into the aortic arch to measure the basal and ACh-induced plasma NO concentration. Vascular nitrotyrosine levels were examined by enzyme-linked immunoassay (ELISA). Both an immunohistochemical study and Western blotting were performed to examine the PPARgamma and gp91phox expression. The cotreatment with pioglitazone significantly suppressed the negative effects of Ang II, that is, the decreases in basal and ACh-induced NO production and the increase in vascular nitrotyrosine levels. Both the immunohistochemical study and Western blotting demonstrated that pioglitazone treatment enhaced PPARgamma expression and greatly inhibited Ang II-induced up-regulation of gp91phox. In conclusion, the PPARgamma agonist pioglitazone significantly improved NO bioavailability in Ang II-infused rabbits, most likely by attenuating nitrosative stresses.

Association of plasma adiponectin levels with oxidative stress in hemodialysis patients

BACKGROUND

Recent evidence suggests that oxidative stress may be an instigator of the metabolic syndrome, and adiponectin, an adipocyte-derived polypeptide, may modulate oxidative stress, ameliorating the atherosclerotic process.

AIM

Oxidative stress is increased in hemodialysis (HD) patients. We hypothesize that a relationship between plasma levels of adiponectin and markers of inflammation and oxidative stress exists.

METHODS AND RESULTS

In 124 HD patients, plasma adiponectin levels and three separate oxidative stress markers, tumor necrosis factor-alpha as well as high-sensitivity C-reactive protein (hsCRP) were determined. Plasma adiponectin was significantly and negatively correlated with serum hsCRP (r = -0.247, p = 0.008) and plasma malondialdehyde (MDA) levels (r = -0.326; p < 0.001). Multiple regression analyses suggested that plasma MDA, serum HDL cholesterol levels and logarithmically transformed hsCRP were the variables independently associated with plasma adiponectin levels.

CONCLUSION

Plasma adiponectin was significantly associated with plasma MDA, serum HDL cholesterol levels and serum hsCRP levels. Our results suggest the possibility that plasma adiponectin may play a role in alleviating oxidative stress in HD patients.

Simultaneous control of hyperglycemia and oxidative stress normalizes endothelial function in type 1 diabetes

OBJECTIVE

Previous studies have shown that in type 1 diabetes endothelial dysfunction persists even when glycemia is normalized. Moreover, oxidative stress has recently been demonstrated to be the mediator of hyperglycemia-induced endothelial dysfunction.

RESEARCH DESIGN AND METHODS

Thirty-six type 1 diabetic patients and 12 control subjects were enrolled. The diabetic patients were divided into three groups. The first group was treated for 24 h with insulin, achieving a near-normalization of glycemia. After 12 h of this treatment, vitamin C was added for the remaining 12 h. The second group was treated for 24 h with vitamin C. After 12 h of this treatment, insulin was started, with achievement of near-normalization of glycemia for the remaining 12 h. The third group was treated for 24 h with both vitamin C and insulin, achieving near-normalization of glycemia.

RESULTS

Neither normalization of glycemia nor vitamin C treatment alone was able to normalize endothelial dysfunction or oxidative stress. However, a combination of insulin and vitamin C normalized endothelial dysfunction and decreased oxidative stress to normal levels.

CONCLUSIONS

This study suggests that long-lasting hyperglycemia in type 1 diabetic patients induces permanent alterations in endothelial cells, which may contribute to endothelial dysfunction by increased oxidative stress even when hyperglycemia is normalized.

The Influence of Free 3-Nitrotyrosine and Saliva on the Quantitative Analysis of Protein-Bound 3-Nitrotyrosine in Sputum

Background

We have recently developed a new technique for quantitatively measuring protein-bound 3-nitrotyrosine (3-NT), a footprint of nitrosative stress, utilizing high-performance liquid chromatography with an electrochemical detection (HPLC-ECD) system. Using this system, we showed that 3-NT formation was upregulated in the sputum of both COPD and asthmatic patients. However, in order to improve the accuracy of the measurement system, We have to resolve some problems which were the influence of free amino acid form of 3-NT and of salivary contamination.

Objectives

We initially investigated the amount of the free amino acid form of 3-NT in induced sputum and compared with that of protein-bound 3-NT. Next, we evaluated the concentration of protein-bound 3-NT in saliva and compared with that in induced sputum by means of HPLC-ECD.

Methods

Five male COPD patients were enrolled. Induced sputum and saliva were obtained from the patients. The free amino acid form of 3-NT in sputum and saliva was measured by HPLC-ECD, and the protein-bound 3-NT and tyrosine in sputum and saliva were enzymatically hydrolyzed by Streptomyces griseus Pronase and measured for the protein hydrolysate by HPLC-ECD.

Results

The mean value of the amount of protein-bound 3-NT was 65.0 fmol (31.2 to 106.4 fmol). On the other hand, the amount of the free amino acid form of 3-NT was under the detection limit (<10 fmol). The levels of both 3-NT (sputum: 0.55 ± 0.15 pmol/ml, saliva: 0.02 ± 0.01 pmol/ml, p < 0.01) and tyrosine (sputum: 0.81 ± 0.43 μmol/ml, saliva: 0.07 ± 0.04 μmol/ml, p < 0.01) in saliva were significantly lower than in sputum. The percentage of 3-NT in saliva to that in sputum was about 3.1%, and that of tyrosine was about 9.0%.

Conclusion

The free amino acid form of 3-NT does not affect the measurement of protein-bound 3-NT. Furthermore, the influence of salivary contamination on the measurement of protein-bound 3-NT in induced sputum by means of HPLC-ECD was very small and could be negligible.

Evaluation of Pharmacological Modulation of Nitroglycerin-Induced Impairment of Nitric Oxide Bioavailability by a Catheter-Type Nitric Oxide Sensor

BACKGROUND

The present study aimed to elucidate the effect of long-term treatment with nitroglycerin (NTG) on the bioavailability of nitric oxide (NO) examined by a catheter-type NO sensor. The study also examined whether these effects could be modified by an antioxidant, an angiotensin converting enzyme inhibitor, or an angiotensin II type 1 receptor antagonist (ARB).

METHODS AND RESULTS

Male New Zealand rabbits were treated for 7 days with NTG patches, either alone or in combination with tempol, enalapril, or valsartan (ARB). The plasma NO concentration was measured with the catheter-type NO sensor. The plasma peroxynitrite concentration was measured by enzyme-linked immunosorbent assay. An increase in plasma NO concentration in response to acetylcholine (ACh) were significantly attenuated in the NTG-treated group as compared with the control. Plasma peroxynitrite concentration in NTG-treated group was significantly higher as compared with the control. The negative effects of NTG were significantly suppressed by the co-treatment with tempol, enalapril or valsartan.

CONCLUSIONS

Chronic treatment of rabbits with NTG elicits the impairment of the ACh-stimulated NO production. In addition, the negative effects of NTG might be prevented by the co-treatment with drugs attenuating nitrosative stress.

Effects of Angiotensin II on NO Bioavailability Evaluated Using a Catheter-Type NO Sensor

We investigated the acute or chronic effects of angiotensin (Ang) II on the bioavailability of NO in Ang II-infused rabbits using the catheter-type NO sensor. Male New Zealand White rabbits were infused with vehicle (sham), Ang II at a rate of 200 ng/kg per minute, either alone or in combination with hydralazine, Ang II type I receptor antagonist (valsartan), or an antioxidant (tempol) for 24 hours or 14 days. Plasma NO concentration was measured using the catheter-type NO sensor located in the aorta. We then infused saline (vehicle) and acetylcholine (ACh) into the aortic arch with or without pretreatment with N(G)-methyl-l-arginine. An increase in plasma NO levels in response to ACh was significantly attenuated in the Ang II group compared wit the control group. The decrease in the basal plasma NO concentration was significantly lower in the Ang II group than in the control group. Plasma peroxynitrite concentrations in Ang II group were significantly higher than in the control group. The negative effects of Ang II, that is, the decrease in basal and ACh-induced NO production and the increase in oxidative stress, were significantly suppressed by the cotreatment with either valsartan or tempol. Short-term treatment with Ang II significantly increased the ACh-induced increase in plasma NO concentration, as well as basal NO release. Although Ang II stimulates release of NO in the short term, chronic treatment with Ang II elicits the decreased NO bioavailability in the aorta of the Ang II-infusion rabbit model.

Measurement and significance of 3-nitrotyrosine in systemic lupus erythematosus

Nitration of free and protein associated tyrosine represents, in vivo, a mechanism that can severely compromise the cell function. The detection of 3-nitrotyrosine (3-NT) in pathological tissues is suggestive of the occurrence of nitrating pathways and has been identified as a marker of inflammation and a stable end product of increased reactive nitrogen intermediate production. Protein nitration occurs in many disease conditions including systemic lupus erythematosus (SLE). In this study we show that the level of both free and protein bound 3-NT, which is produced by reactive nitrogen species (RNS)-dependent oxidative damage, is elevated in patients with SLE and that there is a possible role of RNS-modified epitopes in the aetiology of the disease. Commercially available poly L-tyrosine was exposed to nitrating species, inducing nitration in tyrosine residues. Immunoglobulin-G (IgG) purified on Protein-A-Sepharose matrix from 24 SLE patients was studied for their recognition of native and nitrated poly L-tyrosine by direct binding and competition enzyme-linked immunosorbent assay (ELISA). The formation of immune complex between SLE IgG and nitrated poly L-tyrosine was visualized by gel retardation assay. Free 3-NT in patients' sera was detected and quantitated by high performance liquid chromatography whereas protein-bound 3-NT was analysed by Western blotting and the concentration was calculated by sandwich ELISA. The concentration of free 3-NT was found to be 1.4 +/- 0.09 microm whereas the concentration of protein bound 3-NT was 96.52 +/- 21.12 microm nitrated bovine serum albumin equivalents/mg protein, which was significantly higher when compared with healthy controls. Elevated level of 3-NT was observed in SLE patients using two different techniques, when compared with healthy subjects confirms the overproduction of RNS in the pathogenesis of human SLE.

Oxidized-LDL levels are changed during short-term serum glucose variations and lowered with statin treatment in early Type 2 diabetes: a study of endothelial function and microalbuminuria

AIMS

To investigate the role of HMG-CoA reductase inhibitor (statin) treatment during serum glucose variations on plasma oxidized LDL (ox-LDL) levels in obese patients with early Type 2 diabetes mellitus (T2D) and its relationship to endothelial biomarkers.

METHODS

In a double-blind, randomized crossover study, 15 obese diet-treated T2D patients received cerivastatin (0.4 mg/day) or placebo for 3 months. Circulating ox-LDL levels were measured fasting and during a euglycaemic-hyperinsulinaemic clamp (approximately 5.5 mmol/l; EHC) and a hyperglycemic clamp (approximately 20 mmol/l; HC). An endothelium-dependent flow-mediated dilation (FMD) study was carried out and urinary albumin excretion (UAE) was measured at rest and during EHC. S-ICAM, s-VCAM and basal prothrombotic factors were also measured.

RESULTS

During cerivastatin treatment, basal circulating ox-LDL levels decreased by 48% (P<0.001) compared with placebo. Serum ox-LDL levels decreased during EHC and remained unchanged during HC compared with the fasting state; with cerivastatin treatment these levels were lower compared with placebo both in the fasting state and during the clamp studies. FMD was higher with cerivastatin than with placebo (P<0.001) and the increments in FMD correlated with decrements in serum ox-LDL levels (r=0.78, P=0.001). Microalbuminuria increased during EHC but this was blunted during cerivastatin therapy compared with placebo (P<0.05). Basal sICAM-1 and sVCAM-1 levels decreased (P<0.01 and P<0.05, respectively).

CONCLUSIONS

In early obese Type 2 diabetic patients, serum ox-LDL levels are influenced by short-term serum glucose variations and lowered with cerivastatin therapy. During cerivastatin treatment, improved flow-mediated endothelium-dependent dilation was associated with decrements in circulating ox-LDL levels and the hyperinsulinaemia-induced urinary albumin excretion was blunted.

Effect of arginine deficiency on arginine-dependent post-translational protein modifications in mice

Transgenic mice that overexpress arginase-I in their small-intestinal enterocytes suffer from a pronounced, but selective decrease in circulating arginine levels during the suckling period, resulting in impaired growth and development of hair, muscle and immune system. In the present study, we tested the hypothesis that the arginine-deficiency phenotype is caused by arginine-specific post-translational modifications, namely, an increase in the degree of mono-ADP-ribosylation of proteins because of reduced competition by free arginine residues and/or an increase in protein-tyrosine nitration because of an increased O2- production by NO synthases in the presence of limiting amounts of arginine. Arginine ADP-ribosylation and tyrosine nitration of proteins in the affected organs were assayed by Western blot analysis, using specific anti-ADP-ribosylarginine and protein-nitrotyrosine antisera. The composition of the group of proteins that were preferentially arginine ADP-ribosylated or tyrosine-nitrated in the respective organs was strikingly similar. Arginine-deficient mice differed from their controls in a reduced ADP-ribosylation of a 130 kDa and a 65 kDa protein in skin and an increased protein nitration of an 83 kDa protein in bone marrow and a 250 kDa protein in spleen. Since only 20 % of the visualised proteins were differentially modified in a subset of the affected organs, our findings appear to rule out these prominent arginine-dependent post-translational protein modifications as mediators of the characteristic phenotype of severely arginine-deficient mice.

Comparison of spectrophotometric, HPLC and chemilumines-cence methods for 3-nitrotyrosine and peroxynitrite interaction

We have studied the interaction of 3-nitrotyrosine with peroxynitrite using three different methods; chemiluminescence, spectrophotometry and HPLC. Peroxynitrite-induced luminol or lucigenin chemiluminescence were significantly decreased by 3-nitrotyrosine, in concentration-dependent manners. The intensity of the peroxynitrite spectrum was also markedly reduced in the presence of 3-nitrotyrosine in the spectrophometric assay. However, there was no attenuation of the 3-nitrotyrosine signal in the HPLC assay after mixing with peroxynitrite. The interaction of 3-nitrotyrosine and hypochlorous acid (HOCl) was also studied via the chemiluminescence assay, where the HOCl-induced responses were markedly inhibited by 3-nitrotyrosine. These results suggest that caution should be taken when studying the levels or interactions of 3-nitrotyrosine.

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.

The myth of pulmonary Raynaud's phenomenon: the contribution of pulmonary arterial vasospasm in patients with systemic sclerosis related pulmonary arterial hypertension

OBJECTIVE

To investigate the contribution of cold induced pulmonary vasospasm by peripheral and central cold stimulus in exacerbating pulmonary arterial hypertension (PAH) in patients with systemic sclerosis undergoing cardiac catheterisation.

METHODS

In a prospective pilot study, 21 patients with systemic sclerosis and catheter proven PAH had mean pulmonary artery pressure (mPAP), pulmonary vascular resistance (PVR), and cardiac output (CO) measured before and after peripheral (hand immersion into cold water at 10-15 degrees C for two minutes if tolerated) and central (direct cold water at 4 degrees C injected into the right atrium) cold pressor challenge. Markers of endothelial activation, platelet function, and nitric oxide degradation were measured in blood sampled from the pulmonary artery.

RESULTS

19 of the patients (mean (SD) age, 56 (4) years; baseline mPAP, 34 (8) mm Hg; PVR, 420 (87) dyne.s.cm(-5); CO, 6.4 (1.8) l/min) tolerated cold hand immersion for the maximum two minute duration. All 21 tolerated central cold pressor challenge (three to five injections of 10 ml saline boluses at 4 degrees C). There was no significant change in haemodynamics after cold challenge by either route of provocation. Levels of endothelin-1, von Willebrand factor, fibrinogen, and 3-nitrotyrosine were raised compared with control values in patients with systemic sclerosis but without PAH, but did not change significantly after peripheral cold challenge.

CONCLUSIONS

Pulmonary vasospasm in response to peripheral and centrally administered cold pressor challenge is unlikely to contribute to persistence of pulmonary arterial hypertension in patients with systemic sclerosis.

Plasma and urinary free 3-nitrotyrosine following cardiac angiography procedures with non-ionic radiocontrast media

BACKGROUND

Radiocontrast media (RCM) administration is a common cause of hospital-acquired acute renal failure, especially in high-risk patients, but mechanisms of nephrotoxicity have not been fully elucidated. Reactive oxidant species recently have been shown to play a role in experimental RCM nephropathy, while there is clinical evidence that acetylcysteine, an antioxidant drug, has a protective effect against RCM nephropathy in humans. However, no study has been published showing that RCM administration elicits oxidative stress in humans.

METHODS

In an unselected series of patients undergoing elective cardiac catheterization for coronary artery angiography and/or angioplasty, we monitored the time course of plasma and urinary levels of free 3-nitrotyrosine (3-NT), a stable marker of peroxynitrite generation resulting from the in vivo reaction of superoxide and nitric oxide. Urinary 3-NT levels were measured as the ratio of urinary 3-NT to urinary creatinine. Measurements were taken at baseline, immediately after the procedure and at 24, 48 and 72 h.

RESULTS

Twenty-six patients were studied (median age 67.5 years, range 42-86; baseline serum creatinine 1.0 mg/dl, 0.6-1.5; RCM dose 215 ml, 100-580). Plasma 3-NT levels slightly increased over the 72 h following the procedure (P<0.001), while urinary 3-NT levels peaked at the end of the procedure (P<0.001). Urinary 3-NT levels reached at the end of the procedure were proportional to the RCM dose administered (P = 0.017).

CONCLUSIONS

The present study provides indirect evidence that RCM administration in humans is associated with an increased production of 3-NT. Further studies are needed to ascertain whether oxygen- and nitrogen-derived radical species play a major role in the pathogenesis of RCM-associated nephrotoxicity in the clinical setting.

Use of a novel double-sandwich enzyme-linked immunosorbent assay method for assaying chondroitin sulfate proteoglycans that bear 3-nitrotyrosine core protein modifications, a previously unrecognized proteoglycan modification in hydrocephalus

3-Nitrotyrosine is a useful marker for nitric oxide-mediated tissue injury. However, which proteins are preferred peroxynitrite modification targets is unclear. Chondroitin sulfate proteoglycans (CSPGs) abnormally accumulate in cerebrospinal fluid of human neonates with hydrocephalus and may be a target for peroxynitrite modification. We examined (1). whether CSPG core protein can be modified by peroxynitrite in vitro; (2). to what degree in comparison to bovine serum albumin (BSA), the most commonly used nitrated protein standard; (3). whether nitrated CSPGs can be measured directly in biological samples; and (4). whether nitrated proteoglycan concentrations in cerebrospinal fluid correlate with disease. In vitro nitration of bovine aggrecan was performed by exposure to different peroxynitrite concentrations, and 3-nitrotyrosine products were measured. Bovine serum albumin (BSA) nitration was also performed in comparison. A larger percentage of tyrosine residues were nitrated in aggrecan than in BSA under all conditions tested. An enzyme-linked immunosorbent assay (ELISA) for 3-nitrotyrosine consistently overestimated aggrecan nitration when nitrated BSA was used as the standard. This is important as most current assays of nitration in biological samples use nitrated BSA as the standard. Therefore, if nitrated CPSGs were a substantial portion of the nitrated proteins in a sample, total nitrated protein content would be overestimated. Aggrecan retained its function of binding hyaluronic acid despite substantial nitration. A double-sandwich ELISA was developed for nitrated CSPGs in biological samples, using nitrated aggrecan as standard. [Nitrated CSPG] was found to be significantly elevated in preterm hydrocephalus cerebrospinal fluid (P<0.02), but correlated poorly with cerebrospinal fluid [nitric oxide] (P>0.069), suggesting that nitrated CSPG and NO levels may be independant markers of tissue injury. Peroxynitrite-mediated protein tyrosine nitration is a previously unrecognized modification of CSPGs, and may reflect level of brain injury in hydrocephalus.

Comparison of nitrotyrosine antibodies and development of immunoassays for the detection of nitrated proteins

Three monoclonal antibodies (mAb) and three polyclonal antibodies (pAb) have been characterized and compared with respect to their cross-reactivities and affinities for 3-nitrotyrosine, eight aromatic compounds with similar chemical structures, a peptide containing a single nitrotyrosine residue, and fourteen nitrated protein standards (bovine serum albumin, BSA) containing different numbers of nitrotyrosine residues per protein molecule (0.2 to 16.8). In indirect competitive immunoassays, mAb Alexis 39B6 exhibited the highest affinity for free 3-nitrotyrosine (10(6) L mol(-1)), while the pAb Oxis 24312 from sheep exhibited the highest affinities for nitrated proteins (up to 10(8) L mol(-1)). The apparent affinities determined in the indirect competitive assays were inversely correlated with the limits of detection (LOD) determined in one-sided immunoassays. With the sheep pAb minimum LOD on the order of 10 pmol L(-1) were achieved for highly nitrated proteins, corresponding to effective LOD on the order of 100 pmol L(-1) for nitrotyrosine residues. In the one-sided assays, however, the LOD for nitrated proteins increased proportionally with increasing background concentrations of native proteins in the investigated samples. Sandwich immunoassays combining pAb and mAb for selective enrichment and detection of nitrated proteins allowed to eliminate this native protein matrix effect and to achieve LOD on the order of 300 pmol L(-1) for highly nitrated proteins independent of native protein background concentrations.

A Novel Competitive ELISA for Both Free and Protein-Bound Nitrotyrosine

3-Nitro-L-tyrosine (nitrotyrosine) has recently been considered to be useful as a biomarker of endogenous production of several reactive nitrogen species including peroxynitrite. In the present study, nitrotyrosine was coupled to human serum albumin (HSA) using a two-step glutaraldehyde method and immunized mouse with multifocal intradermal injections. Using a conventional immunization protocol, 12 stable monoclonal antibodies (MAbs) producing cell lines recognizing nitrotyrosine were obtained. Six MAbs were selected for further characterization. A study of cross-reactions with nitrotyrosine-like compounds showed that the antibodies had a high specificity for nitrotyrosine, but no detectable reactivity with L-tyrosine, p-nitro-L-phenylalanine, o-phospho-L-tyrosine or 3-amino-L-tyrosine. Using these high titer and affinity antibodies, a competitive inhibition ELISA was developed with a lower detection limit of approximately 20 nmol/L to detect both free and protein-bound nitrotyrosine in biological systems.

Determination of oxidative protein and lipid damage in adult hypopituitary patients with GH deficiency

The aim of this study is to determine oxidative protein and lipid damage in adult hypopituitary GH-deficient patients. Eighteen hypopituitary GH-deficient--otherwise healthy-adults on conventional replacement therapy other than GH (9 male, 9 female, age 41.8 +/- 16.4 yr) and 18 healthy subjects (6 male, 12 female, age 40.3 +/- 16.2 yr) participated in the study. Plasma products of oxidative protein damage [protein carbonyl (PCO) and nitrotyrozine (NT)], plasma oxidized LDL (oxLDL), plasma product of oxidative lipid damage [lipid hydroperoxide (LHP)] and antioxidant status of the plasma [total thiol (T-SH)] were measured. Body fat percentage, total and LDL-cholesterol concentrations were significantly higher in the hypopituitary group. Plasma PCO, NT, LHP and T-SH concentrations did not differ significantly between patients and controls. OxLDL concentration was significantly higher in the hypopituitary patients (62.4 +/- 17.8 vs 43.1 +/- 11.3 U/l, p = 0.001). In the patients, oxLDL correlated significantly with the duration of hypopituitarism (r = 0.6323, p = 0.01). In the controls, oxLDL correlated significantly with blood pressure, total and VLDL-cholesterol concentrations. Increased oxLDL concentration may indicate increased oxidative stress within the vascular compartment and may contribute to the proatherogenic state in GH-deficient hypopituitary patients independent from conventional risk factors.

Cutting edge: MHC class II-restricted peptides containing the inflammation-associated marker 3-nitrotyrosine evade central tolerance and elicit a robust cell-mediated immune response

Nitrotyrosine is widely recognized as a surrogate marker of up-regulated inducible NO synthase expression at sites of inflammation. However, the potential immunogenicity of autologous proteins containing nitrotyrosine has not previously been investigated. Herein, we used the I-E(K)-restricted T cell epitope of pigeon/moth cytochrome c (PCC/MCC(88-103)) to assess the ability of T cells to recognize ligands containing nitrotyrosine. Substitution of the single tyrosine (Y97) in PCC/MCC(88-103) with nitrotyrosine abrogates recognition by the MCC(88-103)-specific T cell hybridoma 2B4. CBA (H2(K)) mice immunized with MCC(88-103) or nitrated MCC(88-103) peptides produce T cell responses that are mutually exclusive. Transgenic mice that constitutively express PCC under the control of an MHC class I promoter are tolerant toward immunization with MCC(88-103), but exhibited a robust immune response against nitrated MCC(88-103). Analysis of T cell hybridomas specific for nitrated-MCC(88-103) indicated that subtle differences in TCR VDJ gene usage are sufficient to allow nitrotyrosine-specific T cells to escape the processes of central tolerance.

Enzyme immunoassays for the investigation of protein nitration by air pollutants

Two enzyme immunoassays have been developed, characterised, and applied to investigate protein nitration in birch pollen extract (BPE) and bovine serum albumin (BSA) samples exposed to air pollutants. The monoclonal antibody CAY-189542 against nitrotyrosine (raised against peroxynitrite-treated keyhole limpet hemocyanine) was characterised in an indirect competitive assay (affinity and cross-reactivities) and applied in a new one-sided enzyme immunoassay for nitrated proteins. The one-sided assay was calibrated against a nitrated BSA standard with an average of 14 nitrotyrosine residues per molecule (nitro-(14)-BSA; detection limit 8.3 pmol L(-1)), and the sensitivity of the test was found to be significantly enhanced by a multivalent binding mode of the monoclonal antibody (bonus effect of multivalency). The same antibody and a polyclonal antibody against Bet v 1, the most prominent birch pollen allergen, were used in a new sandwich immunoassay for specific determination of nitrated Bet v 1. This assay was calibrated against a nitrated Bet v 1 standard with an average of 3 nitrotyrosine residues per molecule (nitro-(3)-Bet v 1; detection limit 0.2 nmol L(-1)). Bet v 1 and BSA exposed to polluted urban outdoor air and to synthetic gas mixtures containing NO2 and O3 at atmospherically relevant concentration levels were found to be efficiently nitrated within hours to days. Pronounced correlations of nitro-(14)-BSA equivalent concentrations with exposure time and with nitro-(3)-Bet v 1 equivalent concentrations in nitrated BPE samples were observed. Test experiments indicated that the efficiency of protein nitration was strongly enhanced by reactive species formed upon interaction of NO2 with O3 and H2O (e.g. NO3 and HNO3). Potential implications of protein nitration by air pollutants are outlined and discussed.

Postmenopausal hormone replacement therapy use decreases oxidative protein damage

OBJECTIVES

The aim of this study is to evaluate oxidative protein damage (OPD) by investigating protein carbonyl (PCO) and nitrotyrosine (NT) levels, oxidative stress by total thiol (T-SH), erythrocyte glutathione (GSH) and nitric oxide (NO) levels in women receiving hormone replacement therapy (HRT).

MATERIALS AND METHODS

To examine the influence of oxidative stress on OPD, we studied 12 postmenopausal women who had received HRT for 6 months, and 13 postmenopausal women who did not receive HRT, as the control group. All subjects were non-smokers. Blood samples were drawn in the fasting state and processed within 1 h of collection. For NT and NO, serum samples were stored at -70 degrees C until analysis; all other parameters were determined on the same day of collection.

RESULTS

After 6 months, plasma PCO and T-SH levels were decreased, GSH and NO levels were increased, and NT levels were not changed in 12 postmenopausal women receiving HRT. Except the NT levels, the rest of the parameters did not significantly change in the control group. Interestingly, mean NT levels in the control group increased significantly.

CONCLUSIONS

A crucial part of the protective effect of HRT on the cardiovascular system arises secondary to the interaction between estrogen and vessel wall. Our results suggest that an important component of the mechanism underlying this interaction may depend on estrogen's antioxidant effect and its preventive role in OPD.

Relation of aging with oxidative protein damage parameters in the rat skeletal muscle

OBJECTIVES

An increase in oxidative stress may contribute to the development of oxidative protein damage in the aging rat skeletal muscle. Our aim was to reveal protein carbonyl (PCO), advanced oxidation protein products (AOPP), a novel marker of oxidative stress, and protein thiol (P-SH) levels as markers of protein oxidation, as well as lipid hydroperoxide (LHP) levels as a marker of lipid peroxidation, and relation of nitrotyrosine (NT) levels with these markers in skeletal muscle tissue of young, adult, and old male Wistar rats.

DESIGN AND METHODS

In the present study, we investigated the relation between aging and oxidative protein damage parameters such as PCO, NT, AOPP, and P-SH, as well as oxidative stress parameters such as total thiol, nonprotein thiol, and LHP in the skeletal muscle tissue of young, adult, and old Wistar rats.

RESULTS

PCO and NT levels of old rats were significantly increased compared with those of young and adult rats. Skeletal muscle AOPP levels were significantly increased in old rats compared with those of adult rats. P-SH levels were significantly decreased in old rats compared with those of young rats.

CONCLUSIONS

The finding that the increase in PCO levels of young vs. old group was more significant than that of adult vs. old group may suggest that PCO formation is an early specific marker of aging process in skeletal muscle. In addition, increased levels of nitrotyrosine in the skeletal muscle of the old rat group may be a novel specific marker of oxidative protein damage in the aging muscle. The absence of correlation between oxidative protein damage markers mentioned above and LHP levels may indicate that protein oxidation and lipid peroxidation in the aging rat skeletal tissue are two distinct mechanisms.

Accurate quantification of basal plasma levels of 3-nitrotyrosine and 3-nitrotyrosinoalbumin by gas chromatography-tandem mass spectrometry

Measurement of 3-nitro-L-tyrosine (NO(2)Tyr) and protein-related 3-nitro-L-tyrosine in human plasma is associated with numerous methodological problems which result in highly divergent basal plasma levels often ranging within two orders of magnitude. Recently, we have described an interference-free GC-tandem MS-based method for NO(2)Tyr which yielded the lowest basal plasma NO(2)Tyr levels reported thus far. This method was extended to quantify protein-associated 3-nitrotyrosine and in particular 3-nitrotyrosinated albumin (NO(2)TyrALB) in human plasma. NO(2)TyrALB and albumin (ALB) were extracted from plasma by affinity column extraction and digested enzymatically at neutral pH. 3-Nitro- L-[2H(3)]tyrosine was used as internal standard. In plasma of 18 healthy young volunteers the molar ratio of NO(2)TyrALB to albumin-derived tyrosine (TyrALB), i.e. NO(2)TyrALB/TyrALB, was determined to be 1.55+/-0.54x1:10(6) (mean+/-SD). The plasma concentration of NO(2)TyrALB was estimated as 24+/-4 nM. The NO(2)Tyr plasma levels in these volunteers were determined to be 0.73+/-0.53 nM. In the same volunteers, NO(2)TyrALB/TyrALB, NO(2)TyrALB and NO(2)Tyr were measured 15 days later and the corresponding values were determined to be 1.25+/-0.58x1:10(6), 25+/-6 nM and 0.69+/-0.16 nM. For comparison, NO(2)Tyr and NO(2)TyrALB were measured in six plasma samples from healthy volunteers by GC-MS and GC-tandem MS. Different values were found for NO(2)Tyr, i.e. 5.4+/-2.8 versus 2.7+/-1.5 nM, and comparable values for NO(2)TyrALB/TyrALB, i.e. 0.5+/-0.2x1:10(6) versus 0.4+/-0.1x1:10(6), by these methods. The ratio of the values measured by GC-MS to those measured by GC-tandem MS were 2.9+/-3.1 for NO(2)Tyr and 1.2+/-0.2 for NO(2)TyrALB/TyrALB. The present GC-tandem MS method provides accurate values of NO(2)Tyr and NO(2)TyrALB in human plasma.

Preliminary report on nitric oxide-mediated oxidative damage in adolescent varicocele

BACKGROUND

The current study was designed to characterize the process of nitric oxide (NO) and peroxynitrite generation through the determination of nitrotyrosine concentration in the dilated veins of varicoceles in adolescents.

METHODS

Ten adolescents with a median age of 13 years (range 12-17) affected by a left idiopathic varicocele (grade II and III) were studied. Whole blood samples were withdrawn from a peripheral vein at time of induction of anaesthesia, and from a dilated spermatic vein before ligation. Peripheral blood samples from five adolescents undergoing minor surgical procedures were used as controls. The nitrotyrosine concentration was evaluated by a sandwich enzyme-linked immunosorbent assay (ELISA), using a monoclonal anti-nitrotyrosine antibody and Western blot analysis.

RESULTS

Plasma nitrotyrosine concentrations were significantly greater in the spermatic vein when compared with the peripheral vein (P = 0.031). Nitrotyrosine in plasma of controls did not show any significant difference in comparison with peripheral samples from varicocele patients. Western blot analysis confirmed the above data.

CONCLUSIONS

In adolescents with a varicocele, there is an increase in nitrotyrosine concentration within the spermatic vein that can cause protein nitration and cytotoxicity via its reaction with various molecular targets. This could have repercussions on both sperm and testis function. We conclude that an oxidative stress status is present and should be considered as an indication for varicocele treatment in the adolescent.

Role of hyperglycemia in nitrotyrosine postprandial generation

OBJECTIVE

Recently, much attention has been paid to the possibility that postprandial hyperglycemia may be a cardiovascular risk factor in diabetes. Oxidative stress has been involved in the pathogenesis of diabetic complications, and increased plasma levels of nitrotyrosine, a product of peroxynitrite action, have been found in the plasma of diabetic subjects. The aim of the present study was to evaluate whether postprandial hyperglycemia is accompanied by nitrotyrosine generation and, if so, to explore a possible direct role of hyperglycemia in such a phenomenon.

RESEARCH DESIGN AND METHODS

A total of 23 type 2 diabetic patients and 15 matched normal healthy subjects were recruited for this study. Two different tests were performed in diabetic patients: a standard meal preceded by regular insulin (0.15 units/kg body wt) or insulin aspart (0.15 units/kg body wt) to achieve different levels of postprandial hyperglycemia. The meal test was also performed in healthy control subjects. At 0 min and 1, 2, 4, and 6 h after each meal, blood glucose, triglyceride, and nitrotyrosine levels were measured.

RESULTS

Fasting nitrotyrosine was significantly increased in diabetic patients and was further increased during both meal tests in diabetic subjects but not normal subjects. As compared with regular insulin, aspart administration significantly reduced the area under the curve of both glycemia (P < 0.04) and nitrotyrosine (P < 0.03), whereas that of triglycerides was not significantly affected by the treatment.

CONCLUSIONS

This study shows a direct correlation between postprandial hyperglycemia and the production of nitrotyrosine, a marker of oxidative stress, in patients with type 2 diabetes.

Determination of nitrotyrosine and related compounds in biological specimens by competitive enzyme immunoassay

A gas mediator, nitric oxide is converted to peroxynitrite in the presence of superoxide anion. Peroxynitrite is a potent oxidant, which injures various tissues and organs by nitration of the tyrosine residues of proteins, and it enhances the late response of inflammation. The determination of nitrated tyrosine, nitrotyrosine, which is a stable final metabolite of peroxynitrite, provides an important indicator of tissue disorders caused by peroxynitrite. This paper reports a competitive solid-phase immunoassay for measuring nitrotyrosine in various biological specimens. In this study, peroxidase-conjugated nitrotyrosine was prepared by reaction of nitrotyrosine with 1,4-benzoquinone treatment, and then it was allowed to compete with nitrotyrosine on an anti-nitrotyrosine antibody-coated 96-well multiplate. No amino acids or related compounds tested in the experiments interfered with the immune reaction of nitrotyrosine, except cysteine, which only slightly inhibited the immune reaction at the concentrations higher than 1000 times the concentration of nitrotyrosine. The limit of detection of free nitrotyrosine was approximately 500 pg/mL (2 nM) at a competition ratio (B/B(o)%) of 80%. The newly developed enzyme immunoassay (EIA) method was used for assay of nitrotyrosine in biological specimens, with the following results: (i) Lipopolysaccharide (LPS) activation of RAW264.7 cells induced a significant increase in nitrotyrosine production compared to that with nonactivated cells. N(omega)-nitro-L-arginine methyl ester decreased nitrotyrosine production with either LPS-activated or nonactivated RAW cells. There is a relationship between nitrotyrosine production and nitrite ion. (ii) The nitrotyrosine level detected in the plasma specimens from healthy volunteers was 35.21 +/- 4.87 ng/mL (135.4 +/- 18.7 nM). (iii) The concentration of nitrotyrosine in the nasal lavage fluid of allergic rhinitis patients was 41.40 +/- 20.96 ng/mL (159.02 +/- 80.6 nM). Thus, the EIA method combines sensitivity and specificity with the ability to process a large number of specimens to quantify nitrotyrosine produced with in vivo and in vitro sources.

Biochemical markers related to Alzheimer's dementia in serum and cerebrospinal fluid

The diagnosis of Alzheimer's disease (AD) is currently based on clinical and neuropsychological examination. To date there is no blood test available that can discriminate dementia patients from healthy individuals. In the present paper, an overview of the current state of knowledge on biologic markers in serum (plasma) and CSF is presented. The combination of characteristic plaque markers tau and amyloid bèta may constitute a specific and sensitive CSF marker for AD. Glial fibrillary acidic protein and antibodies in CSF may be a marker for severe neurodegeneration. CSF concentrations of the oxidative stress markers 3-nitrotyrosine, 8-hydroxy-2'-deoxyguanosine and isoprostanes are increased in AD patients. Serum 24S-OH-cholesterol may be an early whereas glial fibrillary acidic protein autoantibody level may be a late marker for neurodegeneration. To date, serum alpha(1)-Antichymotripsin concentration is the most convincing marker for CNS inflammation. Increased serum homocysteine concentrations have also been consistently reported in AD. In summary, a large overlap in mean concentrations has been observed in studies comparing AD patients with healthy controls for single markers. These studies together support the theory of testing several serum markers in combination for the diagnosis of AD.

Inducible nitric oxide synthase is expressed in normal human melanocytes but not in melanoma cells in response to tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharide

Nitric oxide is a gaseous messenger involved in the regulation of several physiologic processes in various cell types, including skin cells. Three different nitric oxide synthases (neuronal nitric oxide synthase, endothelial nitric oxide synthase, inducible nitric oxide synthase) have been identified in human cells. For inducible nitric oxide synthase, an inducibility by cytokines and lipopolysaccharides have been found. For murine melanoma cells, a connection between elevated levels of nitric oxide after inducible nitric oxide synthase induction and consequent apoptosis had been described. By northern analysis, we detected inducible nitric oxide synthase mRNA in four of 15 human melanoma cell lines cultured without inducible nitric oxide synthase inducing cytokines. Induction of inducible nitric oxide synthase mRNA by tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharides was seen in normal human melanocytes but not in melanoma cell lines. In accordance, inducible nitric oxide synthase protein expression was clearly inducible in cultures of normal melanocytes, whereas in six melanoma cell lines investigated, inducible nitric oxide synthase was found weakly expressed already before treatment with tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharides, and its expression was not inducible. The apoptotic rates both in normal melanocytes and in two melanoma cell lines (SK-Mel-19 and O-Mel-2) were increased by treatment with tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharides; however, these effects could not be prevented by the specific nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine. These data reveal a clear-cut difference between human melanoma cell lines and cultured normal human melanocytes with respect to inducible nitric oxide synthase inducibility. Although the data do not support the hypothesis that inducible nitric oxide synthase is an important regulator for apoptosis in human melanoma cells, the regulation deficiency found for melanoma cells may be of importance for melanocytic transformation and tumor progression.

Evaluation of 3-nitrotyrosine as a marker for 3-nitropropionic acid-induced oxidative stress in Lewis and Wistar rats and strain-specific whole brain spheroid cultures

The present study investigated whether 3-nitrotyrosine is an early marker for neurodegenerative processes involving oxidative stress. We characterized the 3-nitrotyrosine formation after 3-nitropropionic acid (3-NP) exposure in the whole brain spheroid culture model and in a rat model, using Lewis and Wistar rats. Increased 3-nitrotyrosine concentration in spheroid cultures from Lewis rats was observed at lower dose of and shorter exposure time to 3-NP as compared to alterations in glial fibrillary acidic protein concentration, decrease in glutamine synthetase activity or cell loss. Five days of exposure to 3-NP (5 mM) resulted in decreased staining of GABAergic processes, while neuronal nitric oxide synthase staining was preserved. In addition, staining of EAAC1, anti-2',3'-cyclic nucleotide 3'-phosphohydrolase and ED1 was diminished after treatment of spheroid cultures with 3-nitropropionic acid (5 mM), while isolectin B4 staining was increased. Dithiothreitol and vitamin E inhibited the increased formation of 3-nitrotyrosine. Interestingly, N(G)-nitro-L-arginine methyl ester increased the 3-nitrotyrosine formation. No increased 3-nitrotyrosine concentration was shown after exposure to 3-nitropropionic acid during 5 days in spheroid cultures obtained from Wistar rats. In the striatum of 3-NP-exposed Lewis and Wistar rats, no change in 3-nitrotyrosine concentration was observed, whereas only in Wistar rats the glial fibrillary acidic protein concentration was increased in addition to activation of microglial cells. It is concluded that 3-nitrotyrosine was a more sensitive marker for oxidative stress-induced neurodegeneration than glial fibrillary acidic protein and glutamine synthase in spheroid cell cultures of Lewis rats. Finally, the similarities between the 3-NP spheroid model and the vivo model indicate that the spheroid cultures provide a good alternative for chronic exposure of animals to neurotoxins.

Immunodetection of 3-nitrotyrosine in the liver of zymosan-treated rats with a new monoclonal antibody: comparison to analysis by HPLC

Zymosan-induced peritonitis is associated with an increased production of reactive nitrogen oxides that may contribute to the often-observed failure of multiple organ systems in this model of acute inflammation. Quantitative biochemical evidence is provided for a marked 13-fold increase in protein-bound 3-nitrotyrosine (NTyr), a biomarker of reactive nitrogen oxides, in liver tissue of zymosan-treated rats. In order to investigate the localization of NTyr in this affected tissue, a monoclonal antibody, designated 39B6, was raised against 3-(4-hydroxy-3-nitrophenylacetamido) propionic acid-bovine serum albumin conjugate and its performance characterized. 39B6 was judged by competition ELISA to be approximately 2 orders of magnitude more sensitive than a commercial anti-NTyr monoclonal antibody. Binding characteristics of 39B6 were similar, but not identical, to that of a commercial affinity-purified polyclonal antibody in ELISA and immunohistochemical analyses. Western blot experiments revealed high specificity of 39B6 against NTyr and increased immunoreactivity of specific proteins from liver tissue homogenates of zymosan-treated rats. Immunohistochemical analysis of liver sections indicated a marked zymosan-induced increase in immunofluorescent staining, which was particularly intense in or adjacent to nonparenchymal cells, but not in the parenchymal cells of this tissue. Quantitative analysis of fractions enriched in these cell populations corroborated the immunofluorescent data, although the relative amounts detected in response to zymosan treatment was greatly reduced compared to whole liver tissue. These results demonstrate the high specificity of the newly developed antibody and its usefulness in Western blot and immunohistochemical analysis for NTyr, confirm the presence of NTyr by complementary methods, and suggest the possible involvement of reactive nitrogen oxides in hepatic vascular dysfunction.

Lack of influence of dietary nitrate/nitrite on plasma nitrotyrosine levels measured using a competitive inhibition of binding ELISA assay

The action of peroxynitrite in vivo has been proposed to account for the involvement of nitrotyrosine in the pathogenesis of many diseases. However, it has been demonstrated that nitrite under acidic conditions, similar to those in the human stomach, also has the ability to nitrate tyrosine. Dietary nitrate is also implicated in the progression of gastritis and gastric cancer and elevated levels of nitrate are found in many disease states in which nitrotyrosine may play a role. Thus, we investigated whether the dietary nitrate intake might contribute towards the plasma protein-bound levels of nitrotyrosine. Seven healthy, non-smokers participated in a two-day study consisting of a nitrate-low control day followed by a day during which three nitrate-rich meals were consumed. Maximal urinary excretion was attained 4-6 hours after consumption of a meal and the maximum was proportional to the dose. Plasma nitrate was elevated nine-fold, 1 hour after consumption of a meal containing 128.3 mg nitrate. Plasma nitrated protein levels did not appear to alter significantly from basal 1 hour after supplementation with a nitrate-rich meal. Thus dietary nitrate does not appear to contribute to the levels of plasma nitrated proteins, as determined using a competitive inhibition of binding ELISA assay, but this does not preclude any contribution it may make to the total body burden of nitrotyrosine.

The mechanisms for nitration and nitrotyrosine formation in vitro and in vivo: impact of diet

The detection of 3-nitro-L-tyrosine residues associated with many disease states, including gastric cancer, has implicated a role for peroxynitrite in vivo, and thus endogenously produced nitric oxide and superoxide. Additionally, dietary nitrate has been suggested to be involved in the pathogenesis of gastric cancer through a mechanism involving reduction to nitrite and subsequent formation of potentially mutagenic nitroso-compounds. Studies have now demonstrated that a multitude of reactive nitrogen species other than peroxynitrite are capable of producing nitrotyrosine. Thus, we have reviewed the evidence that dietary nitrate, amongst other reactive nitrogen species, may contribute to the body burden of nitrotyrosine.

Tyrosine nitration: localisation, quantification, consequences for protein function and signal transduction

The nitration of free tyrosine or protein tyrosine residues generates 3-nitrotyrosine the detection of which has been utilised as a footprint for the in vivo formation of peroxynitrite and other reactive nitrogen species. The detection of 3-nitrotyrosine by analytical and immunological techniques has established that tyrosine nitration occurs under physiological conditions and levels increase in most disease states. This review provides an updated, comprehensive and detailed summary of the tissue, cellular and specific protein localisation of 3-nitrotyrosine and its quantification. The potential consequences of nitration to protein function and the pathogenesis of disease are also examined together with the possible effects of protein nitration on signal transduction pathways and on the metabolism of proteins.

Unraveling peroxynitrite formation in biological systems

Peroxynitrite promotes oxidative damage and is implicated in the pathophysiology of various diseases that involve accelerated rates of nitric oxide and superoxide formation. The unambiguous detection of peroxynitrite in biological systems is, however, difficult due to the combination of a short biological half-life, limited diffusion, multiple target molecule reactions, and participation of alternative oxidation/nitration pathways. In this review, we provide the conceptual framework and a comprehensive analysis of the current experimental strategies that can serve to unequivocally define the existence and quantitation of peroxynitrite in biological systems of different levels of organization and complexity.

Relation of oxidative protein damage and nitrotyrosine levels in the aging rat brain

An increase in oxidative stress may contribute to the development of oxidative protein damage in the aging rat brain. In the present study, we investigated the relation between nitrotyrosine levels and other oxidative protein damage parameters such as protein carbonyl and protein thiol, as well as oxidative stress parameters such as total thiol, nonprotein thiol, and lipid hydroperoxides in the brain tissue of young, adult, and old Wistar rats. Brain nitrotyrosine levels of old rats were significantly decreased compared with those of young rats. Young and adult rats were not significantly different as far as these parameters were concerned, however, brain protein carbonyl and lipid hydroperoxide levels of old rats were significantly increased compared with those of young and adult rats. On the other hand, brain tissue total thiol, nonprotein thiol, and protein thiol levels of old rats were significantly decreased compared with those of young and adult rats. The strong correlation we found between protein carbonyl and lipid hydroperoxide levels indicates a striking relation between protein oxidation and lipid peroxidation in the aging brain tissue. The results of this study suggest that protein carbonyl formation is both a sensitive and a specific marker of brain aging. However, decreased nitrotyrosine levels in old rats, in contradiction to the expected, may be due to mechanisms other than oxidative protein damage in the aging rat brain.

In vitro production of peroxynitrite by haemocytes from marine bivalves: C-ELISA determination of 3-nitrotyrosine level in plasma proteins from Mytilus galloprovincialis and Crassostrea gigas

BACKGROUND

Peroxynitrite is increasingly proposed as a contributor to defence system in marine bivalve. It can be formed by combination of superoxide and nitric oxide, and can react with tyrosine residues of proteins giving rise to 3-nitrotyrosine.

RESULTS

The present article describes a competitive ELISA for the measurement of 3-nitrotyrosine contents of plasma proteins from marine bivalves by means of a monoclonal anti 3-nitrotyrosine antibody mouse IgG.

CONCLUSIONS

This assay is sensitive enough to determine the amounts of 3-nitrotyrosine in plasma proteins from one animal only. Using the C-ELISA, we have shown that the phagocytosis of zymosan particles increased the 3-nitrotyrosine levels of plasma proteins from mussel M. galloprovincialis and oyster C. gigas 5.8 and 7.5 times respectively.

Oxidative protein damage in early stage Type 1 diabetic patients

To examine the influence of oxidative stress on oxidative protein damage, we studied 51 young Type 1 diabetic patients clinically free of complications and 48 healthy normolipidaemic age-matched controls. We determined: (1) plasma carbonyl (PCO), plasma total thiol (T-SH), and nitrotyrosine (NT) levels as markers of oxidative protein damage; (2) plasma lipid hydroperoxide (LHP), and nitric oxide (NO) levels as markers of oxidative stress; (3) plasma total antioxidant capacity (TAO), ceruloplasmin (Cp), transferrin (TRF), unsaturated iron binding capacity (UIBC), erythrocyte glutathione (GSH), and erythrocyte superoxide dismutase (SOD) as markers of free radical scavengers. There were no significant differences in the levels of these markers between prepubertal diabetic patients and the controls. The levels of both of PCO and LHP were increased in adolescent and young adult Type 1 diabetic patients with respect to their controls. In the adolescent group, patient versus control values for PCO were 1.04+/-0.067 versus 0.67+/-0.0274 nmol/mg and for LHP they were 2. 10+/-1.09 versus 1.00+/-0.4 nmol/mg. In the young adult group, patient versus control values for PCO were 0.99+/-0.054 versus 0. 66+/-0.02 nmol/mg and for LHP they were 1.96+/-0.78 versus 1.15+/-0. 4 nmol/mg. TAO levels were significantly decreased in adolescent diabetic patients compared to their controls (0.92+/-0.27 vs. 1. 86+/-0.37) and in young adult diabetic patients compared to their controls (0.80+/-0.27 vs. 2.11+/-0.54 nmol/mg). T-SH was not different between diabetic patients and the controls. Serum NT, NO, and erythrocyte SOD levels were not different either between three groups of diabetic patients or between the patients and their controls. We attribute this lack of difference to limited disease duration. Changes in markers of oxidative stress other than NT, NO, and SOD observed in adolescent and young adult early stage Type 1 diabetic patients contribute to the imbalance in the redox status of the plasma. We attribute this imbalance to metal-catalyzed protein oxidation in both groups of Type 1 diabetic patients clinically free from complications.

Relative reactivity of lysine and other peptide-bound amino acids to oxidation by hypochlorite

Antibacterial and inflammatory responses of neutrophils and macrophages produce hypochlorite as a major oxidant. Numerous side chains of amino acids found in extracellular proteins can be modified by hypochlorite, including His, Arg, Tyr, Lys, Trp, and Met. We studied the relative reactivity of each of these amino acid residues in short N-blocked peptides, where other residues in the peptide were highly resistant to hypochlorite attack. Hypochlorite treatment led to modified peptides in each case, which were detected by changes in retention on reversed-phase HPLC. A distinct single product, consuming two equivalents of hypochlorite per equivalent of peptide, was obtained from the Lys-containing peptides. UV spectroscopy, nuclear magnetic resonance (NMR), and electrospray/mass spectroscopy identified this product as the dichloramine at the epsilon-amino group of the Lys side chain. The dichloramine at Lys did not decompose to form a detectable amount of carbonyl reactive with dinitrophenylhydrazine. The dichloramine at Lys did however quantitatively revert back to Lys during HCl digestion of the tetrapeptide for amino acid analysis, with simultaneous modification of the adjacent Phe residue. The formation of the dichloramine at Lys was not blocked by peptides or acetylated amino acids that contained Tyr, His, or Arg. In contrast, the presence of equimolar Met-containing peptide, or N-Acetyl-Trp, both inhibited the formation of the dichloramine at Lys. Thus, Met and Trp side chains of proteins might be able to protect Lys from chloramine formation under some circumstances, but this interpretation must consider that Met and Trp are typically found in relatively inaccessible hydrophobic sites, whereas lysine is typically exposed on the protein surface. The hierarchy of amino acid reactivities examined here will aid in the prediction of residues in biological samples most likely to be modified by hypochlorite.

Oxidative protein damage in type I diabetic patients with and without complications

To examine the influence of oxidative stress on oxidative protein damage, we studied 47 Type I diabetic patients with and without complications. We determined plasma protein carbonyl, plasma protein thiol and nitrotyrosine levels as markers of oxidative protein damage, plasma lipid hydroperoxide levels as markers of oxidative stress, and plasma total thiol, plasma nonprotein thiol, erythrocyte glutathione, plasma ceruloplasmin, transferrin and total iron binding capacity as markers of free radical scavenging. There were no significant differences in nitrotyrosine, total plasma thiol, protein thiol, and erythrocyte glutathione levels between diabetic patients with complications and without complications. However, plasma protein carbonyl, lipid hydroperoxide, and nonprotein thiol levels were significantly increased in diabetic patients with complications compared with diabetic patients without complications. Although redox status of plasma is impaired in diabetic patients, we suppose these significantly different markers reflect enhanced oxidative protein damage in diabetic patients with complications.