Nitrite and nitrate analyses: a clinical biochemistry perspective

Influence of Long-Term Anti-Seizure Medications on Redox Parameters in Human Blood

BACKGROUND

Epilepsy is a chronic brain disease affecting millions of people worldwide, but little is known about the impact of anti-seizure medications on redox homeostasis.

METHODS

This study aimed to compare the effects of the long-term use of oral anti-seizure medications in monotherapy (lamotrigine, carbamazepine, and valproate) on antioxidant enzymes: superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, haemoglobin, and methaemoglobin content in erythrocytes, and concentrations of total proteins and thiols, nitrites, lipid peroxides and total glutathione in the plasma of epilepsy patients and drug-naïve patients.

RESULTS

The results showed that lamotrigine therapy led to lower superoxide dismutase activity (p < 0.005) and lower concentrations of total thiols (p < 0.01) and lipid peroxides (p < 0.01) compared to controls. On the other hand, therapy with carbamazepine increased nitrite levels (p < 0.01) but reduced superoxide dismutase activity (p < 0.005). In the valproate group, only a decrease in catalase activity was observed (p < 0.005). Canonical discriminant analysis showed that the composition of antioxidant enzymes in erythrocytes was different for both the lamotrigine and carbamazepine groups, while the controls were separated from all others.

CONCLUSIONS

Monotherapy with anti-seizure medications discretely alters redox homeostasis, followed by distinct relationships between antioxidant components.

Association of urinary nitrate with diabetes complication and disease-specific mortality among adults with hyperglycemia

BACKGROUND

The hyperglycemia condition disrupts the metabolism of nitrate/nitrite and nitric oxide, and dietary nitrate intake can restore nitric oxide homeostasis. This study aims to examine whether urinary nitrate is associated with diabetes complications and long-term survival among people with hyperglycemia.

METHODS

A total of 6208 people with hyperglycemia who participated in the National Health and Nutrition Examination Survey from 2005 to 2014 were enrolled. Diabetes complications included congestive heart failure, coronary heart disease, angina, stroke, myocardial infarction, diabetic retinopathy, and nephropathy. Mortality wasobtained from the National Death Index until 2015. Urinary nitrate was measured by ion chromatography coupled with electrospray tandem mass spectrometry, which was log-transformed and categized into tertiles. Logistic regression models and cox proportional hazards models were respectively performed to assess the association of urinary nitrate with the risk of diabetes complications and disease-specific mortalities.

RESULTS

After adjustment for potential confounders including urinary perchlorate and thiocyanate, compared with the participants in the lowest tertile of nitrate, the participants in the highest tertile had lower risks of congestive heart failure(odd-ratio[OR] = 0.41, 95%CI:0.27-0.60) and diabetic nephropathy(OR = 0.50, 95%CI: 0.41-0.62). Meanwhile, during a total follow-up of 41,463 person-year, the participants in the highest tertile had lower mortality risk of all-cause(hazard-ratio[HR] = 0.78, 95%CI:0.62-0.97), cardiovascular disease(CVD)(HR = 0.56, 95%CI:0.37-0.84) and diabetes(HR = 0.47, 95%CI:0.24-0.90), which showed dose-dependent linear relationships(P for non-linearity > 0.05). Moreover, no association between nitrate and cancer mortality was observed(HR = 1.13, 95%CI:0.71-1.80).

CONCLUSIONS

Higher urinary nitrate is associated with lower risk of congestive heart failure and diabetic nephropathy, and lower risk of all-cause, CVD, and diabetes mortalities. These findings indicated that inorganic nitrate supplementation can be considered as a supplementary treatment for people with hyperglycemia.

TRPA1 Polymorphisms Modify the Hypotensive Responses to Propofol with No Change in Nitrite or Nitrate Levels

Anesthesia with propofol is frequently associated with hypotension. The TRPA1 gene contributes to the vasodilator effect of propofol. Hypotension is crucial for anesthesiologists because it is deleterious in the perioperative period. We tested whether the TRPA1 gene polymorphisms or haplotypes interfere with the hypotensive responses to propofol. PCR-determined genotypes and haplotype frequencies were estimated. Nitrite, nitrates, and NOx levels were measured. Propofol induced a more expressive lowering of the blood pressure (BP) without changing nitrite or nitrate levels in patients carrying CG+GG genotypes for the rs16937976 TRPA1 polymorphism and AG+AA genotypes for the rs13218757 TRPA1 polymorphism. The CGA haplotype presented the most remarkable drop in BP. Heart rate values were not impacted. The present exploratory analysis suggests that TRPA1 genotypes and haplotypes influence the hypotensive responses to propofol. The mechanisms involved are probably other than those related to NO bioavailability. With better genetic knowledge, planning anesthesia with fewer side effects may be possible.

Direct and specific analysis of nitrite and nitrate in biological and non-biological samples by capillary ion analysis for the rapid identification of fatal intoxications with sodium nitrite

In recent years, a significant increase of reports about suicidal cases due to intentional sodium nitrite intake has been described. In the forensic pathology context, the strategy to approach intoxication cases by sodium nitrite, without any preliminary information or hint, is not straightforward. Indeed, in a number of cases the lack of crime scene data and/or specific pathological signs makes difficult the identification of nitrite poisoning. Moreover, the analytical determination of nitrite in blood is challenging, due to its rapid oxidization to nitrate by hemoglobin. Although several methods have been proposed for the clinical analysis of nitrate and/or nitrite in biological samples, none of these is specifically focused on the determination of these ions in cadaveric samples. Consequently, the diagnosis of nitrite fatal intoxication is still based on methemoglobin analysis. The present paper reports the optimization and validation of an analytical method of capillary ion analysis (CIA) with UV detection, for the determination of nitrite and nitrate in biological fluids and its application to two authentic cases of death by nitrite intake. The analyses were carried out in a bare fused-silica capillary (75 µm inner diameter) using 100 mM sodium tetraborate (pH 9.24) as background electrolyte and applying a voltage of - 15 kV between the capillary ends. The detection was obtained by direct UV absorption recorded at 214 nm wavelength. Bromide was used as the internal standard. Linearity was established in the range of 0.25-5 mmol/L). Reproducibility (intraday and day-to-day) was characterized by relative standard deviations (RSDs) 14.7% for peak areas. The method was applied to the determination of nitrite and nitrate in two real forensic cases, where high concentrations of nitrate were found in cadaveric blood samples (6.5 and 4.4 mmol/L, respectively). Nitrite was found only in trace amounts, due to the instability of this ion in cadaveric blood where it is oxidized to nitrate. The present method represents a new tool for the direct and rapid determination of nitrite and nitrate in cases of forensic interest, and thus offers a diagnostic tool more sensitive and precise than the need methemoglobin analysis.

Structural and morphological tuning of Cu-based metal oxide nanoparticles by a facile chemical method and highly electrochemical sensing of sulphite

A facile one-step chemical method is introduced for the successful synthesis of Cu₂O, CuO and CuNa₂(OH)₄ crystal structures and their electrochemical properties were also investigated. X-ray diffraction studies revealed that these copper-based oxide nanoparticles display different crystal structures such as cubic (Cu₂O), monoclinic (CuO) and orthorhombic [CuNa₂(OH)₄]. The microstructural information of nanoparticles was investigated by transmission electron microscopy. It shows attractive morphologies of different orientation such as rod like structure, nanobeads and well-aligned uniform nanorod for Cu₂O, CuO and CuNa₂(OH)₄, respectively. Electrochemical sensing of sulphite (SO₃²⁻) on these three copper-based oxide modified electrodes was investigated. Among the three different crystal structures, CuO shows promising electrocatalytic activity towards oxidation of sulphite. A linear variation in peak current was obtained for SO₃²⁻ oxidation from 0.2 to 15 mM under the optimum experimental condition. The sensitivity and detection limit were in the order of 48.5 µA cm⁻² mM⁻¹ and 1.8 µM, respectively. Finally, practical utility of CuO modified electrode was demonstrated for the estimation of sulphite in commercial wine samples.

Arginase II polymorphisms modify the hypotensive responses to propofol by affecting nitric oxide bioavailability

PURPOSE

Propofol anesthesia is usually accompanied by hypotensive responses, which are at least in part mediated by nitric oxide (NO). Arginase I (ARG1) and arginase II (ARG2) compete with NO synthases for their common substrate L-arginine, therefore influencing the NO formation. We examined here whether ARG1 and ARG2 genotypes and haplotypes affect the changes in blood pressure and NO bioavailability in response to propofol.

METHODS

Venous blood samples were collected from 167 patients at baseline and after 10 min of anesthesia with propofol. Genotypes were determined by polymerase chain reaction. Nitrite concentrations were measured by using an ozone-based chemiluminescence assay, while NO_x (nitrites + nitrates) levels were determined by using the Griess reaction.

RESULTS

We found that patients carrying the AG + GG genotypes for the rs3742879 polymorphism in ARG2 gene and the ARG2 GC haplotype show lower increases in nitrite levels and lower decreases in blood pressure after propofol anesthesia. On the other hand, subjects carrying the variant genotypes for the rs10483801 polymorphism in ARG2 gene show more intense decreases in blood pressure (CA genotype) and/or higher increases in nitrite levels (CA and AA genotypes) in response to propofol.

CONCLUSION

Our results suggest that ARG2 variants affect the hypotensive responses to propofol, possibly by modifying NO bioavailability.

TRIAL REGISTRATION

NCT02442232.

Associations of endothelial biomarkers, nitric oxide metabolites and endothelin, with blood pressure and coronary lesions depend on cardiovascular risk and sex to mark endothelial dysfunction on the SCORE scale

OBJECTIVES

Endothelial dysfunction contributes to the onset and progression of cardiovascular diseases. However, direct associations of vasoactive mediators with cardiovascular risk are poorly understood.

METHODS

We have determined associations of circulating levels of stable metabolites of nitric oxide, nitrate and nitrite (NOx), endothelin-1, and the endothelin-1/NOx ratio with blood pressure in 177 asymptomatic subjects without signs of coronary atherosclerosis; associations with blood pressure and with presence of coronary lesions were also evaluated in 457 patients suspected to have coronary heart disease with or without coronary lesions confirmed by coronary angiography. All participants were on a low nitrate diet 24 h prior to blood sampling.

RESULTS

In men, NOx levels were inversely correlated with blood pressure similar to women with low (0-4%) European Systematic Coronary Risk Estimation (SCORE). However, the correlation was not significant in women with high SCORE (5-8%). High systolic blood pressure over 140 mm Hg was negatively associated with NOx levels in asymptomatic men (p=0.05) but not in women. This association is disrupted in male and female patients with coronary atherosclerosis. In male patients, NOx (p=0.05), endothelin (p=0.01), and the endothelin/NOx ratio (p=0.04) were associated with presence of coronary lesions.

CONCLUSIONS

Thus, elevated cardiovascular risk according to SCORE over 4% in asymptomatic women, but not in men, is associated with a shift in markers of endothelial dysfunction. Presence of coronary lesions in patients is associated with significant changes in circulating levels of markers of endothelial dysfunction in men but not in women.

Urinary nitrate concentration as a marker for kidney transplant rejection

BACKGROUND

Early identification and treatment of kidney transplant rejection episodes is vital to limit loss of function and prolong the life of the transplanted kidney and recipient. Current practice depends on detecting a creatinine rise. A biomarker to diagnose transplant rejection at an earlier time point than current practice, or to inform earlier decision making to biopsy, could be transformative. It has previously been shown that urinary nitrate concentration is elevated in renal transplant rejection. Nitrate is a nitric oxide (NO) oxidation product. Transplant rejection upregulates NO synthesis via inducible nitric oxide synthase leading to elevations in urinary nitrate concentration. We have recently validated a urinary nitrate concentration assay which could provide results in a clinically relevant timeframe. Our aim was to determine whether urinary nitrate concentration is a useful tool to predict renal transplant rejection in the context of contemporary clinical practice.

METHODS

We conducted a prospective observational study, recruiting renal transplant participants over an 18-month period. We made no alterations to the patients' clinical care including medications, immunosuppression, diet and frequency of visits. We collected urine samples from every clinical attendance. We assessed the urinary nitrate to creatinine ratio (uNCR) between patient groups: routine attendances, biopsy proven rejection, biopsy proven no rejection and other call backs. uNCR was examined over time for those with biopsy proven transplant rejection. These four groups were compared using an ANOVA test.

RESULTS

A total of 2656 samples were collected. uNCR during biopsy proven rejection, n = 15 (median 49 μmol/mmol, IQR 23-61) was not significantly different from that of routine samples, n = 164 (median 55 μmol/mmol, IQR 37-82) (p = 0.55), or biopsy proven no rejection, n = 12 (median 39 μmol/mmol, IQR 21-89) (P = 0.77). Overall uNCR was highly variable with no diagnostic threshold for kidney transplant rejection. Furthermore, within-patient uNCR was highly variable over time, and thus it was not possible to produce individualised patient thresholds to identify rejection. The total taking Tacrolimus was 204 patients, with no statistical difference between the uNCR of all those on Tacrolimus, against those not, p = 0.18.

CONCLUSION

The urinary nitrate to creatinine ratio is not a useful biomarker for renal transplant rejection.

Spatial and temporal distribution characteristics of different forms of inorganic nitrogen in three types of rivers around Lake Taihu, China

In order to control nitrogen (N) pollution of Lake Taihu, China, we studied the spatial and temporal distribution characteristics of inorganic N in inflowing rivers polluted by industry, agriculture, and domestic sewage during low, moderate, and high flow periods. The results showed that dissolved total nitrogen (DTN) was the main fraction of total nitrogen (TN) input from these rivers. Inflowing rivers had distinct impacts on TN, DTN, ammonium N (NH₄⁺), and nitrate N (NO₃^-) concentrations of Lake Taihu during the low flow period. Particulate nitrogen (PN) had an impact on Lake Taihu during the three flow periods and all the three types of rivers would increase PN concentration in the lake. Rivers polluted by agriculture had the greatest impact on Lake Taihu's TN, DTN, NO₃^-, and dissolved inorganic N (DIN) concentrations, while rivers polluted by industry had the greatest impact on NH₄⁺ concentration. Therefore, agriculture and industry should be key targets for nutrient reductions. The in-lake N concentrations were higher than those of inflowing rivers during moderate and high flow periods.

A quasi-reagentless point-of-care test for nitrite and unaffected by oxygen and cyanide

The ubiquitous nitrite is a major analyte in the management of human health and environmental risks. The current analytical methods are complex techniques that do not fulfil the need for simple, robust and low-cost tools for on-site monitoring. Electrochemical reductase-based biosensors are presented as a powerful alternative, due to their good analytical performance and miniaturization potential. However, their real-world application is limited by the need of anoxic working conditions, and the standard oxygen removal strategies are incompatible with point-of-care measurements. Instead, a bienzymatic oxygen scavenger system comprising glucose oxidase and catalase can be used to promote anoxic conditions in aired environments. Herein, carbon screen-printed electrodes were modified with cytochrome c nitrite reductase together with glucose oxidase and catalase, so that nitrite cathodic detection could be performed by cyclic voltammetry under ambient air. The resulting biosensor displayed good linear response to the analyte (2–200 µM, sensitivity of 326 ± 5 mA M⁻¹ cm⁻² at −0.8 V; 0.8–150 µM, sensitivity of 511 ± 11 mA M⁻¹ cm⁻² at −0.5 V), while being free from oxygen interference and stable up to 1 month. Furthermore, the biosensor’s catalytic response was unaffected by the presence of cyanide, a well-known inhibitor of heme-enzymes.

Nitrite-induced testicular toxicity in rats: therapeutic potential of walnut oil

Objective:

To determine the impact of walnut oil on nitrite-induced testicular toxicity in Sprague-Dawley (SD) rats. Available evidence suggests that walnut oil contains high levels of important unsaturated fatty acids including alpha-linolenic acid (ALA) and omega-3; nitrite is a reproductive toxicant that causes the loss of germ cells in the seminiferous tubules and generates oxidative stress in the testes, thus reducing sperm counts and affecting sperm morphology.

Methods:

This study included 24 male and 24 female adult SD rats. The male rats randomly assigned to Group A (controls) were given normal saline 2 ml/kg. The rats in Groups B, C, and D were given 50mg/kg body weight (bwt) of walnut oil, 0.08 mg/kg bwt of nitrite, and 0.08 mg/kg bwt of nitrite + 50 mg/kg of walnut oil respectively for 28 days via gastric gavage. Tested parameters included: testicular histology, sperm parameters, reproductive hormones, fertility, malondialdehyde (MDA), superoxide dismutase (SOD), reduced glutathione, and catalase (CAT).

Results:

A severe decrease in spermatogenic cell series, hypocellularity, tubular atrophy, decreased sperm quality, and increased MDA levels were observed in the rats given nitrite only when compared to controls. Rats given 50 mg/kg of walnut oil had significant growth of seminiferous epithelium compared to controls. The rats given walnut oil and nitrite had significant growth of seminiferous epithelium, improved sperm quality, and had decreased MDA levels.

Conclusion:

Walnut oil attenuated the deleterious effects of nitrite to the testes, reduced oxidative stress, and promoted spermatogenesis.

Angiotensin converting enzyme inhibitors enhance the hypotensive effects of propofol by increasing nitric oxide production

Propofol anesthesia is usually accompanied by hypotension. Studies have shown that the hypotensive effects of propofol increase in patients treated with angiotensin-converting enzyme inhibitors (ACEi). Given that both propofol and ACEi affect nitric oxide (NO) signaling, the present study tested the hypothesis that ACEi treatment induces pronounced hypotensive responses to propofol by increasing NO bioavailability. In this study we evaluated 65 patients, divided into three groups: hypertensive patients chronically treated with ACEi (HT-ACEi; n = 21), hypertensive patients treated with other antihypertensive drugs instead of ACEi, such as angiotensin II receptor blockers, β-blockers or diuretics (HT; n = 21) and healthy normotensive subjects (NT; n = 23). Venous blood samples were collected at baseline and after 10min of anesthesia with propofol 2mg/kg administrated intravenously by bolus injection. Hemodynamic parameters were recorded at each blood sample collection. Nitrite levels were determined by using an ozone-based chemiluminescence assay, while NOx (nitrites+nitrates) levels were measured by using the Griess reaction. Additionally, experimental approaches were used to validate our clinical findings. Higher decreases in blood pressure after propofol anesthesia were observed in HT-ACEi group as compared with those found in NT and HT groups. Consistently, rats treated with the ACEi enalapril showed more intense hypotensive responses to propofol. The hypotensive effects of propofol were associated with increased NO production in both clinical and experimental approaches. Enhanced increases in nitrite levels after propofol anesthesia were observed in HT-ACEi patients compared with NT and HT groups. Accordingly, rats treated with enalapril showed increased vascular NO formation after propofol anesthesia compared with rats receiving vehicle. Our data show that ACEi enhance the hypotensive responses to propofol anesthesia and increase nitrite concentrations. These findings suggest that increased NO bioavailability may account for the enhanced hypotensive effects of propofol in ACEi-treated patients.

Nitric Oxide in the Pathogenesis and Treatment of Tuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is globally known as one of the most important human pathogens. Mtb is estimated to infect nearly one third of the world's population with many subjects having a latent infection. Thus, from an estimated 2 billion people infected with Mtb, less than 10% may develop symptomatic TB. This indicates that the host immune system may constrain pathogen replication in most infected individuals. On entering the lungs of the host, Mtb initially encounters resident alveolar macrophages which can engulf and subsequently eliminate intracellular microbes via a plethora of bactericidal mechanisms including the generation of free radicals such as reactive oxygen and nitrogen species. Nitric oxide (NO), a key anti-mycobacterial molecule, is detected in the exhaled breath of patients infected with Mtb. Recent knowledge regarding the regulatory role of NO in airway function and Mtb proliferation paves the way of exploiting the beneficial effects of this molecule for the treatment of airway diseases. Here, we discuss the importance of NO in the pathogenesis of TB, the diagnostic use of exhaled and urinary NO in Mtb infection and the potential of NO-based treatments.

Serum nitrite and nitrate levels, NOx, can predict cardiovascular mortality in the elderly in a 3-year follow-up study

Nitric oxide (NO) is an important functional regulator that contributes to progression of various cardiovascular diseases. We studied associations between nitric oxide metabolites, nitrite and nitrate (NOx), and cardiovascular mortality in a prospective 3-year follow-up cohort study in 1,869 elderly patients aged over 55 years. The Cox proportional hazard regression model was adjusted for multiple factors including sex, age, risk corresponding to preexisting cardiovascular conditions, and serum inflammatory markers (C-reactive protein, interleukin-6, fibrinogen, and leucocytes count). During the follow-up period, there were a total of 348 deaths including 216 deaths unrelated to cardiovascular events and 132 cardiovascular deaths. Cox regression adjusted for factors related to cardiovascular disease risks and inflammatory markers showed a significant association between high levels of serum nitric oxide metabolites, NOx, and increased cardiovascular mortality (hazard ratio 2.21; 95% confidence interval 1.13-4.31) but there was no association with non-cardiovascular mortality. Analysis of adjusted hazard ratios demonstrates that association of serum nitric oxide metabolites with cardiovascular mortality was independent of levels of inflammatory markers. Thus, elevated concentrations of serum nitric oxide metabolites are a predictor of cardiovascular mortality and may be used as an integral marker of cardiovascular death. © 2016 BioFactors, 43(1):82-89, 2017.

High oxidative stress adversely affects NFκB mediated induction of inducible nitric oxide synthase in human neutrophils: Implications in chronic myeloid leukemia

Increasing evidence support bimodal action of nitric oxide (NO) both as a promoter and as an impeder of oxygen free radicals in neutrophils (PMNs), however impact of high oxidative stress on NO generation is less explored. In the present study, we comprehensively investigated the effect of high oxidative stress on inducible nitric oxide synthase (iNOS) expression and NO generation in human PMNs. Our findings suggest that PMA or diamide induced oxidative stress in PMNs from healthy volunteers, and high endogenous ROS in PMNs of chronic myeloid leukemia (CML) patients attenuate basal as well as LPS/cytokines induced NO generation and iNOS expression in human PMNs. Mechanistically, we found that under high oxidative stress condition, S-glutathionylation of NFκB (p50 and p65 subunits) severely limits iNOS expression due to its reduced binding to iNOS promoter, which was reversed in presence of DTT. Furthermore, by using pharmacological inhibitors, scavengers and molecular approaches, we identified that enhanced ROS generation via NOX2 and mitochondria, reduced Grx1/2 expression and GSH level associated with NFκB S-glutathionylation in PMNs from CML patients. Altogether data obtained suggest that oxidative status act as an important regulator of NO generation/iNOS expression, and under enhanced oxidative stress condition, NOX2-mtROS-NFκB S-glutathionylation is a feed forward loop, which attenuate NO generation and iNOS expression in human PMNs.

Stable isotope-assisted LC-MS/MS monitoring of glyceryl trinitrate bioactivation in a cell culture model of nitrate tolerance

The nitric oxide (NO) metabolites nitrite (NO2(-)) and nitrate (NO3(-)) can be quantified as an endpoint of endothelial function. We developed a LC-MS/MS method of measuring nitrite and nitrate isotopologues, which has a lower limit of quantification (LLOQ) of 1 nM. This method allows for isotopic labeling to differentiate newly formed nitrite and nitrate from nanomolar to micromolar background levels of nitrite and nitrate in biological matrices. This method utilizes 2,3-diaminonaphthalene (DAN) derivatization, which reacts with nitrite under acidic conditions to produce 2,3-naphthotriazole (NAT). NAT was chromatographically separated on a Shimadzu LC System with an Agilent Extend-C18 5 μm 2.1 × 150 mm column and detected using a multiple reaction monitoring (MRM) method on an ABSciex 3200 QTRAP mass spectrometer operated in positive mode. Mass spectrometry allows for the quantification of (14)N-NAT (m/z 170.1) and (15)N-NAT (m/z 171.1). Both nitrite and nitrate demonstrated a linear detector response (1 nM - 10 μM, 1 nM - 100 nM, respectively), and were unaffected by common interferences (Dulbecco's Modified Eagle Medium (DMEM), fetal bovine serum (FBS), phenol red, and NADPH). This method requires minimal sample preparation, making it ideal for most biological applications. We applied this method to develop a cell culture model to study the development of nitrate tolerance in human endothelial cells (EA.hy926).

Endothelial nitric oxide synthase: From biochemistry and gene structure to clinical implications of NOS3 polymorphisms

Nitric oxide (NO) is an important vasodilator with a well-established role in cardiovascular homeostasis. While mediator is synthesized from L-arginine by neuronal, endothelial, and inducible nitric oxide synthases (NOS1,NOS3 and NOS2 respectively), NOS3 is the most important isoform for NO formation in the cardiovascular system. NOS3 is a dimeric enzyme whose expression and activity are regulated at transcriptional, posttranscriptional,and posttranslational levels. The NOS3 gene, which encodes NOS3, exhibits a number of polymorphic sites including single nucleotide polymorphisms (SNPs), variable number of tandem repeats (VNTRs), microsatellites, and insertions/deletions. Some NOS3 polymorphisms show functional effects on NOS3 expression or activity, thereby affecting NO formation. Interestingly, many studies have evaluated the effects of functional NOS3 polymorphisms on disease susceptibility and drug responses. Moreover, some studies have investigated how NOS3 haplotypes may impact endogenous NO formation and disease susceptibility. In this article,we carried out a comprehensive review to provide a basic understanding of biochemical mechanisms involved in NOS3 regulation and how genetic variations in NOS3 may translate into relevant clinical and pharmacogenetic implications.

Homocysteine and nitrite levels are modulated by MTHFR 677C>T polymorphism in obese women treated with simvastatin

Higher homocysteine (Hcy) levels are associated with cardiovascular risk. The aim of the present study was to evaluate the effect of simvastatin treatment on circulating Hcy levels in obese women without hypertension, diabetes or dyslipidaemia; and to determine whether the 677C>T polymorphism located in methylenetetrahydrofolate reductase (NAD(P)H) (MTHFR) gene modulates the effects of this treatment on Hcy and nitrite (as a biomarker of nitric oxide (NO) bioavailability). Twenty-five obese women (body mass index ≥ 30 kg/m(2) ) who had received 20 mg/day simvastatin for 6 weeks were enrolled in the study. Venous blood samples were collected to measure plasma biomarkers and gene polymorphisms. Simvastatin treatment significantly reduced total cholesterol, low-density lipoprotein-cholesterol, thiobarbituric acid-reactive substances, high-sensitivity C-reactive protein and Hcy, whereas nitrite levels were increased. The reduction in Hcy levels in carriers of the T allele was -20.3% compared with -9.4% in patients with the CC genotype. Importantly, before treatment, nitrite levels were significantly higher in patients with the CC genotype compared with T allele carriers, whereas after treatment these levels were similar between groups. Our findings demonstrate that obese women without comorbidities and carrying the T variant of the 677C>T polymorphism of MTHFR exhibit benefits with simvastatin treatment, mainly in terms of increased NO levels.

Construction of effective disposable biosensors for point of care testing of nitrite

In this paper we aim to demonstrate, as a proof-of-concept, the feasibility of the mass production of effective point of care tests for nitrite quantification in environmental, food and clinical samples. Following our previous work on the development of third generation electrochemical biosensors based on the ammonia forming nitrite reductase (ccNiR), herein we reduced the size of the electrodes' system to a miniaturized format, solved the problem of oxygen interference and performed simple quantification assays in real samples. In particular, carbon paste screen printed electrodes (SPE) were coated with a ccNiR/carbon ink composite homogenized in organic solvents and cured at low temperatures. The biocompatibility of these chemical and thermal treatments was evaluated by cyclic voltammetry showing that the catalytic performance was higher with the combination acetone and a 40°C curing temperature. The successful incorporation of the protein in the carbon ink/solvent composite, while remaining catalytically competent, attests for ccNiR's robustness and suitability for application in screen printed based biosensors. Because the direct electrochemical reduction of molecular oxygen occurs when electroanalytical measurements are performed at the negative potentials required to activate ccNiR (ca.-0.4V vs Ag/AgCl), an oxygen scavenging system based on the coupling of glucose oxidase and catalase activities was successfully used. This enabled the quantification of nitrite in different samples (milk, water, plasma and urine) in a straightforward way and with small error (1-6%). The sensitivity of the biosensor towards nitrite reduction under optimized conditions was 0.55 A M(-1) cm(-2) with a linear response range 0.7-370 μM.

The Determination of Nitrate and Nitrite in Human Urine and Blood by High-Performance Liquid Chromatography and Cloud-Point Extraction

A simple efficient and practical separation/preconcentration coupled with HPLC method for the determination nitrate and low concentrations of nitrite in human urine and blood was investigated. The method is based on precolumn derivatization using the Griess reaction and cloud-point extraction (CPE) of nitrite anion and direct determination of nitrate using its UV absorbance by ion-pair HPLC. The chromatographic process with detection at two wavelengths (510 and 220 nm) allows the determination of nitrite and nitrate. Decolorization and protein precipitation of urine and blood was applied to overcome the interference of matrix and enhance the sensitivity. The method was validated for linearity, accuracy and precision. Under the optimum conditions, the linear range of nitrite from 10 to 1,000 ng/mL and nitrate from 0.1 to 10 µg/mL. Product recoveries ranged from 92.4 to 99.9%. The limits of detection were 1 ng/mL and 0.1 µg/mL for nitrite and nitrate, respectively. Therefore, the technique was simple and reliable, with potential application in biological sample analysis of nitrate and nitrite.

Serum nitrate and nitrite levels in patients with hypertension and ischemic stroke depend on diet: a multicenter study

OBJECTIVES

Nitric oxide, NO, is the key vasorelaxing agent produced by vascular endothelium. Stable end products of NO oxidation, nitrate and nitrite (NOx), are considered as markers of endothelial dysfunction associated with hypertension. Our goal was to compare NOx levels in patients with hypertension on controlled low nitrate diet with NOx levels in general population without dietary restrictions.

PATIENTS AND METHODS

The study included 1005 participants split into 8 groups: healthy subjects (n=28) and patients with moderate (n=37) and malignant hypertension (n=24) on low nitrate diet; healthy subjects (n=9) and patients with stroke (n=44) on low nitrate diet; normotensive subjects (n=354) and patients with elevated blood pressure (n=430) and severe hypertension (n=79) without dietary restrictions.

RESULTS

In groups with controlled low NOx diet, patients with moderate and malignant hypertension had significantly (p<0.01) higher serum NOx versus healthy subject (66.9±18.8μM and 75.3±22.7μM versus 52.8±28.8μM, respectively). Patients with stroke had significantly (p=0.02) higher serum NOx levels versus corresponding group of healthy subjects (106.3±58.4μM versus 71.2±18.1μM, respectively). In the absence of dietary control, differences in serum NOx levels between normotensive subjects and patients with elevated blood pressure and severe hypertension were not significant (p>0.1).

CONCLUSION

Differences in serum NOx concentrations are associated with severity of hypertension only in patients on low nitrate diet. The highest concentrations of NOx were observed in patients with stroke. In the absence of dietary control, NOx levels were not associated with presence or severity of hypertension.

Possible mechanism of generation of nitrite and non-thiolate nitroso compounds in blood plasma during inflammatory processes

Generation of nitrite (NO2¯) and non-thiolate nitroso compounds in human blood during leukocyte activation mainly occurred due to destruction of NO donors in the plasma, but not due to intensification of NO synthesis. We proposed a mechanism of production of nitrite and non-thiolate nitroso compounds in the blood during inflammation.

Plasma levels of nitric oxide metabolites are markedly reduced in normotensive men with electrocardiographically determined left ventricular hypertrophy

Recent studies have revealed that electrocardiographically determined left ventricular hypertrophy (ECG-LVH) is a risk factor for cardiovascular death not only in hypertensive patients but also in normotensive subjects. However, the underlying mechanisms remain to be elucidated. In this study, we tested our hypothesis that normotensive subjects with ECG-LVH have reduced nitric oxide production. A total of 840 Japanese male workers were enrolled, and 579 eligible subjects were studied. ECG-LVH was assessed according to the Sokolow-Lyon voltage criteria and the Cornell voltage-duration product. The median level of plasma NOx (nitrite plus nitrate), a marker of systemic nitric oxide production, was markedly lower in the normotensive subjects with ECG-LVH (n=73) than in those without (n=506), and the clinical characteristics were significantly different between the 2 groups (each P<0.05). Importantly, a one-to-one propensity score matching analysis showed similar markedly lower median plasma NOx level in the normotensive subjects with ECG-LVH compared with that observed in the matched normotensive subjects without ECG-LVH (P<0.05). Furthermore, the tertiles of the plasma NOx levels were inversely correlated with the prevalence and severity of ECG-LVH (both P<0.05). The lower plasma NOx levels were associated with significantly higher plasma 8-isoprostane levels, a marker of systemic lipid peroxidation (P<0.05). These results provide the first evidence that normotensive subjects with ECG-LVH exhibit defective nitric oxide production, along with increased oxidative stress. Our findings may thus explain, at least in part, a potential mechanism underlying the increased risk of cardiovascular death in normotensive individuals with ECG-LVH.

Effect of short-term low-intensity exercise training on association of oxygen free radicals and nitric oxide production in patients with acute myocardial infarction

Moderate-to-high intensity of exercise training within 2 to 3 months decreases oxygen free radicals (reactive oxygen species, ROS) and increases nitric oxide (NO) in outpatients with myocardial infarction. There is no data about the association of ROS and NO after short-term low-intensity exercise training within 5 days in patients hospitalized with acute myocardial infarction (AMI). A total of 32 male patients with AMI were randomized into two groups: 15 patients with short-term low-intensity exercise training within 5 days formed the training group and 17 patients without such exercise training formed the control group. All patients performed exercise treadmill test with modified Bruce protocol before and after the study. F2-isoprostane and NO concentration of the training group increased slightly after modified Bruce exercise treadmill test. Compared with the control group, NO of the training group was also slightly higher. Baseline NO and uric acid were negative predictor variables for F2-isoprostane in all patients hospitalized with AMI, and triglyceride was a positive predictor variable. After the study, physical capacity of the training group was higher; but heart rate and systolic blood pressure were lower significantly. This study showed that short-term low-intensity exercise training for patients hospitalized with AMI did not change ROS and NO productions, but it improved physical capacity and lowered heart rate and systolic blood pressure. NO was negative predictor variable for F2-isoprostane in controlling ROS changes in dynamic compensation mechanism.

Nitrite and catalase levels rule oxidative stability and safety properties of milk: a review

This review focuses on recent evidence showing that various types of udder inflammation (mastitis) are associated with increased concentration of NO˙-derived metabolites, nitrite and nitrate, and oxidatively modified organic components under commercial farming and experimental conditions.

Oxidative stress in diabetes: implications for vascular and other complications

In recent decades, oxidative stress has become a focus of interest in most biomedical disciplines and many types of clinical research. Increasing evidence shows that oxidative stress is associated with the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure. Based on these studies, an emerging concept is that oxidative stress is the “final common pathway” through which the risk factors for several diseases exert their deleterious effects. Oxidative stress causes a complex dysregulation of cell metabolism and cell–cell homeostasis; in particular, oxidative stress plays a key role in the pathogenesis of insulin resistance and β-cell dysfunction. These are the two most relevant mechanisms in the pathophysiology of type 2 diabetes and its vascular complications, the leading cause of death in diabetic patients.

Cells and mediators of inflammation (C-reactive protein, nitric oxide, platelets and neutrophils) in the acute and convalescent phases of uncomplicated Plasmodium vivax and Plasmodium falciparum infection

The haematological changes and release of soluble mediators, particularly C-reactive protein (CRP) and nitric oxide (NO), during uncomplicated malaria have not been well studied, especially in Brazilian areas in which the disease is endemic. Therefore, the present study examined these factors in acute (day 0) and convalescent phase (day 15) patients infected with Plasmodium falciparum and Plasmodium vivax malaria in the Brazilian Amazon. Haematologic parameters were measured using automated cell counting, CRP levels were measured with ELISA and NO plasma levels were measured by the Griess reaction. Our data indicate that individuals with uncomplicated P. vivax and P. falciparum infection presented similar inflammatory profiles with respect to white blood cells, with high band cell production and a considerable degree of thrombocytopaenia during the acute phase of infection. Higher CRP levels were detected in acute P. vivax infection than in acute P. falciparum infection, while higher NO was detected in patients with acute and convalescent P. falciparum infections. Although changes in these mediators cannot predict malaria infection, the haematological aspects associated with malaria infection, especially the roles of platelets and band cells, need to be investigated further.

Assessment of oxidative status markers and NO bioavailability in hypertensive disorders of pregnancy

The systemic oxidative status in hypertensives disorders of pregnancy (HDP) and its association with endothelial dysfunction is controversial. In the present study, we evaluated systemic plasma levels of oxidative stress markers (TBARS (thiobarbituric acid-reactive substances) and carbonyl) and total antioxidant status (FRAP (ferric reducing ability of plasma (ferric reducing/antioxidant power) and reduction of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide))), as well as assessed the impact these markers have on nitric oxide (NO) status in healthy pregnant (HP, n=38), gestational hypertensive (GH, n=33) and preeclamptic pregnant women (PE, n=28). We found similar values of TBARS among all groups, and reduced carbonyl levels in HDP between the PE and GH. Conversely, significant increases in plasma activity of antioxidant status were observed in the GH and PE groups compared to the HP group (using both MTT or FRAP method). Importantly, HDP present significantly lower nitrite levels compared to HP women. In Conclusion, our findings show a compensatory antioxidant mechanism against reactive oxygen species (ROS) generation in HDP, which is not associated with nitrite levels restoration.