Analysis of nitrate in biological fluids by capillary electrophoresis

Angiotensin-(1-9) reduces cardiovascular and renal inflammation in experimental renin-independent hypertension

Hypertension-induced cardiovascular and renal damage can be mediated by activation of the renin-angiotensin-aldosterone system. There are different factors beyond renin-angiotensin-aldosterone system involved in hypertension and renal damage. Inflammation has emerged as an important mediator of hypertension and cardiovascular and kidney damage. Angiotensin-(1-9), a peptide of the renin-angiotensin system, counter-regulates both the physiological and pathological actions of angiotensin II. Recent data has shown that angiotensin-(1-9) protects the heart and blood vessels from adverse cardiovascular remodeling in experimental models of hypertension and/or heart failure and reduces cardiac fibrosis in stroke-prone, spontaneously hypertensive rats. These effects are mediated by the angiotensin II type 2 receptor (AT2R). However, it remains unknown whether angiotensin-(1-9) also has an anti-inflammatory effect. In the present study, we investigate whether angiotensin-(1-9) reduces inflammation and fibrosis in the heart, arteries, and kidney in a DOCA-salt hypertensive model and explore the mechanisms underlying the amelioration of end-organ damage. DOCA-salt hypertensive rats received: a) vehicle, b) angiotensin-(1-9), c) PD123319 (AT2R blocker), d) angiotensin-(1-9) plus A779 (a Mas receptor blocker) or e) angiotensin-(1-9) plus PD123319, and sham rats were used as a control. Our results showed that angiotensin-(1-9) decreased hypertension and increased vasodilation in DOCA-salt hypertensive rats. These actions were partially inhibited by PD123319. Moreover, angiotensin-(1-9) decreased diuresis, fibrosis, and inflammation. These beneficial effects were not mediated by Mas or AT2R blockers. We concluded that angiotensin-(1-9) protects against volume overload-induced hypertensive cardiovascular and kidney damage by decreasing inflammation in the heart, aortic wall, and kidney, through mechanisms independent of the Mas or AT2R.

Behavior of Listeria monocytogenes in Sliced Ready-to-Eat Meat Products Packaged under Vacuum or Modified Atmosphere Conditions

The objective of this research was to determine the behavior of Listeria monocytogenes in three types of sliced ready-to-eat meat products packaged under vacuum or modified atmosphere conditions and stored at three temperatures. Slices of about 25 g of chorizo (a fermented dry pork sausage), jamón (cured ham), and cecina (a salted, dried beef product) were inoculated with L. monocytogenes NCTC 11994. Slices were packaged in a vacuum or in a modified atmosphere (20% CO2, 80% N2). After packaging, samples were stored for 6 months at three temperatures: 3, 11, or 20°C. Microbiological analyses were performed after 0, 1, 7, 15, 30, 45, 90, and 180 days of storage. The type of meat product, the type of packaging, the temperature, and the day of storage all influenced microbial levels (P < 0.001). L. monocytogenes counts decreased throughout the course of storage in samples of chorizo (quick decrease) and jamón (gradual decrease). In cecina samples, counts of L. monocytogenes increased from day 0 to day 1 of storage and then remained constant until day 90 of the study. These results may be of use for enhancing the safety of these ready-to-eat meat product types. Additional evaluation of the behavior of L. monocytogenes in cecina is needed.

Microchip electrophoresis with amperometric detection method for profiling cellular nitrosative stress markers

The overproduction of nitric oxide (NO) in cells results in nitrosative stress due to the generation of highly reactive species such as peroxynitrite and N2O3. These species disrupt the cellular redox processes through the oxidation, nitration, and nitrosylation of important biomolecules. Microchip electrophoresis (ME) is a fast separation method that can be used to profile cellular nitrosative stress through the separation of NO and nitrite from other redox-active intracellular components such as cellular antioxidants. This paper describes a ME method with electrochemical detection (ME-EC) for the separation of intracellular nitrosative stress markers in macrophage cells. The separation of nitrite, azide (interference), iodide (internal standard), tyrosine, glutathione, and hydrogen peroxide (neutral marker) was achieved in under 40 s using a run buffer consisting of 7.5 to 10 mM NaCl, 10 mM boric acid, and 2 mM TTAC at pH 10.3 to 10.7. Initially, NO production was monitored by the detection of nitrite (NO2(-)) in cell lysates. There was a 2.5- to 4-fold increase in NO2(-) production in lipopolysaccharide (LPS)-stimulated cells. The concentration of NO2(-) inside a single unstimulated macrophage cell was estimated to be 1.41 mM using the method of standard additions. ME-EC was then used for the direct detection of NO and glutathione in stimulated and native macrophage cell lysates. NO was identified in these studies based on its migration time and rapid degradation kinetics. The intracellular levels of glutathione in native and stimulated macrophages were also compared, and no significant difference was observed between the two conditions.

Angiotensin-(1-9) reverses experimental hypertension and cardiovascular damage by inhibition of the angiotensin converting enzyme/Ang II axis

BACKGROUND

Little is known about the biological effects of angiotensin-(1-9), but available evidence shows that angiotensin-(1-9) has beneficial effects in preventing/ameliorating cardiovascular remodeling.

OBJECTIVE

In this study, we evaluated whether angiotensin-(1-9) decreases hypertension and reverses experimental cardiovascular damage in the rat.

METHODS AND RESULTS

Angiotensin-(1-9) (600  ng/kg per min for 2 weeks) reduced already-established hypertension in rats with early high blood pressure induced by angiotensin II infusion or renal artery clipping. Angiotensin-(1-9) also improved cardiac (assessed by echocardiography) and endothelial function in small-diameter mesenteric arteries, cardiac and aortic wall hypertrophy, fibrosis, oxidative stress, collagen and transforming growth factor type β - 1 protein expression (assessed by western blot). The beneficial effect of angiotensin-(1-9) was blunted by coadministration of the angiotensin type 2(AT2) receptor blocker PD123319 (36  ng/kg per min) but not by coadministration of the Mas receptor blocker A779 (100  ng/kg per min). Angiotensin-(1-9) treatment also decreased circulating levels of Ang II, angiotensin-converting enzyme activity and oxidative stress in aorta and left ventricle. Whereas, Ang-(1-9) increased endothelial nitric oxide synthase mRNA levels in aorta as well as plasma nitrate levels.

CONCLUSION

Angiotensin-(1-9) reduces hypertension, ameliorates structural alterations (hypertrophy and fibrosis), oxidative stress in the heart and aorta and improves cardiac and endothelial function in hypertensive rats. These effects were mediated by the AT2 receptor but not by the angiotensin-(1-7)/Mas receptor axis.

Improved separation and detection of picolinic acid and quinolinic acid by capillary electrophoresis-mass spectrometry: application to analysis of human cerebrospinal fluid

"Quinolinic acid (QA)", a metabolite of the kynurenine pathway (KP), is implicated as a major neurological biomarker, which causes inflammatory disorders, whereas there is an increase evidence of the role of picolinic acid (PA) in neuroinflammation. Therefore, there is an urgent need to develop new clinical test for early diagnosis of neuroinflammatory disorders. A comparison is made between three different platforms such as high performance liquid chromatography-electrospray mass spectrometry (HPLC-ESI-MS/MS), nano LC-Chip/ESI-MS/MS, as well as the use of cationic (quaternary ammonium) and anionic (sulfonated) coated capillaries in capillary electrophoresis (CE)-ESI-MS/MS. The comparison revealed that CE-ESI-MS/MS method using a quaternary ammonium coated capillary is the best method for analysis of PA and QA. A simple stacking procedure by the inclusion of acetonitrile in the artificial cerebrospinal fluid (CSF) sample was employed to improve the peak shape and sensitivity of KP metabolites in CE-ESI-MS/MS. The developed CE-ESI-MS/MS assay provided high resolution, high specificity and high sensitivity with a total analysis time including sample preparation of nearly 12 min. In addition, excellent intra-day and inter-day repeatability of migration times and peak areas of the metabolites were observed with respective relative standard deviation (RSD) of less than 2.0% and 2.5%. Somewhat broader variations in repeatability for a 3 independently prepared coated capillary (total 35 runs each) with % RSD up to 3.8% and 5.8% was observed for migration time and peak areas, respectively. Artificial CSF was used as a surrogate matrix to simultaneously generate calibration curves over a concentration range of 0.02-10 μM for PA and 0.4-40 μM for QA. The method was then successfully applied to analyze PA and QA in human CSF, demonstrating the potential of this CE-ESI-MS/MS method to accurately quantitate with high specificity and sensitivity.

Arteriovenous differences in NO2- kinetics in anesthetized rabbits

Despite of the importance of plasma NO2- as an index of endothelial nitric oxide (NO) formation and a substrate for NO production, only a limited kinetic knowledge is available in vivo. To address this issue, we intravenously injected NaNO2 into anesthetized rabbits and quantified changes in arterial and venous plasma NO2- levels. Plasma NO2- levels in arterial blood (956 +/- 220 nM) were slightly, but significantly, higher than those in venous blood (889 +/- 214 nM) under control conditions. Although similar half-lives of the NO2- were observed in arterial and venous plasma, significant arteriovenous differences were observed in the volume of distribution of the central compartment (0.158 +/- 0.007 l/kg in arterial blood and 0.295 +/- 0.015 l/kg in venous blood) and the peripheral compartment (0.259 +/- 0.035 l/kg in arterial blood and 0.135 +/- 0.034 l/kg in venous blood). When NOR1 (authentic NO) was injected, increases in NO2- levels were greater in arterial plasma, and decreases in blood pressure significantly correlated with arterial NO2- levels only (r = 0.90, p < 0.01). These results indicate that changes in NO2- are larger and more easily detectable as an index of NO formation in arterial plasma.

Bioanalytical profile of the L-arginine/nitric oxide pathway and its evaluation by capillary electrophoresis

This review briefly summarizes recent progress in fundamental understanding and analytical profiling of the L-arginine/nitric oxide (NO) pathway. It focuses on key analytical references of NO actions and the experimental acquisition of these references in vivo, with capillary electrophoresis (CE) and high-performance capillary electrophoresis (HPCE) comprising one of the most flexible and technologically promising analytical platform for comprehensive high-resolution profiling of NO-related metabolites. Another aim of this review is to express demands and bridge efforts of experimental biologists, medical professionals and chemical analysis-oriented scientists who strive to understand evolution and physiological roles of NO and to develop analytical methods for use in biology and medicine.

Quantification of iodide and sodium-iodide symporter inhibitors in human urine using ion chromatography tandem mass spectrometry

We developed a sensitive and selective method for quantifying nitrate, thiocyanate, perchlorate and iodide in human urine using ion chromatography coupled with electrospray ionization tandem mass spectrometry. Analysis of proficiency testing materials and spiked urine indicates that the method is precise (coefficients of variation <5%) and accurate (relative percent differences <7.9%). Analytical response was linear across the physiologically relevant concentration range for the analytes, and adequately sensitive to quantify the analytes in >99% of urine samples tested. Measurement of these four toxicologically-related analytes in one assay will provide useful information for assessing potential linkage between exposure and health effects.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips

Poor sensitivity is considered to be one of the major limitations of electrophoretic separation methods, particularly when compared to traditional liquid chromatographic techniques. To address this issue, various in-line preconcentration techniques have been developed over the past 15 years, ranging in power and complexity, and there are now a number of well understood approaches routinely capable of providing a 10,000- to 100,000-fold increase in sensitivity, as well as several that can be pushed above a million. Furthermore, these have been achieved with particularly troublesome and often difficult samples, such as those having high salinity from a biological or environmental origin. This review will discuss the most common methods for improving the sensitivity of CE, CEC and microchip version of these, with particular attention to those approaches developed over the last five years.

Nitrite is an alternative source of NO in vivo

In this study, we investigated whether orally administered nitrite is changed to NO and whether nitrite attenuates hypertension in a dose-dependent manner. We utilized a stable isotope of [15N]nitrite (15NO2−) as a source of nitrite to distinguish between endogenous nitrite and that exogenously administered and measured hemoglobin (Hb)-NO as an index of circulating NO in whole blood using electron paramagnetic resonance (EPR) spectroscopy. When 1 mg/kg Na15NO2was orally administered to rats, an apparent EPR signal derived from Hb15NO ( AZ= 23.4 gauss) appeared in the blood. The peak blood HbNO concentration occurred at the first measurement after intake (5 min) for treatment with 1 and 3 mg/kg (HbNO: 4.93 ± 0.52 and 10.58 ± 0.40 μM, respectively) and at 15 min with 10 mg/kg (HbNO: 38.27 ± 9.23 μM). In addition, coadministration of nitrite (100 mg/l drinking water) with Nω-nitro-l-arginine methyl ester (l-NAME; 1 g/l) for 3 wk significantly attenuated the l-NAME-induced hypertension (149 ± 10 mmHg) compared with l-NAME alone (170 ± 13 mmHg). Furthermore, this phenomenon was associated with an increase in circulating HbNO. Our findings clearly indicate that orally ingested nitrite can be an alternative to l-arginine as a source of NO in vivo and may explain, at least in part, the mechanism of the nitrite/nitrate-rich Dietary Approaches to Stop Hypertension diet-induced hypotensive effects.

Application of capillary zone electrophoresis to the analysis and to a stability study of nitrite and nitrate in saliva

The applicability of capillary zone electrophoresis for the determinations of nitrite and nitrate was studied. Using direct UV detection the limit of detection values of the analytes were 0.14 and 0.21 microg/mL, respectively. The developed method was found to be useful to directly determine nitrite, nitrate and thiocyanate in saliva. It was found that adjusting the pH of the sample to 11 and storing the saliva at 4 degrees C was adequate to make constant the nitrite/nitrate ratio in saliva samples at least 7 days.

High sensitivity analysis of nitrite and nitrate in biological samples by capillary zone electrophoresis with transient isotachophoretic sample stacking

Tissue level of nitrate and nitrite are established indicators of altered nitric oxide metabolism under various pathological conditions. Determination of these anions in biological samples, in the presence of high chloride concentration, using capillary zone electrophoresis suffers from poor detection sensitivity. Separation conditions providing excellent resolution and submicromolar detection sensitivity of nitrate and nitrite have been developed and validated. Simple sample preparation was applied that maintains nitrite stability in tissue extracts and at the same time allows transient isotachophoresis stacking of the analytes. Nitrate and nitrite concentrations in rat brain and liver tissue samples were determined in control and lipopolysaccharide treated animals.

Spin trapping of nitric oxide with the iron-dithiocarbamate complex: chemistry and biology

This brief review describes chemical and biological aspects concerning spin trapping of nitric oxide (NO) with the iron-dithiocarbamate (Fe-DTC) complex as a spin trap. Knowledge on basic properties of the Fe-DTC complex would help in understanding the applicability and limitation of the Fe-DTC-based NO spin-trapping method when it is employed in viable biological systems.

Nitrite-mediated protection against hypochlorous acid-induced chondrocyte toxicity: a novel cytoprotective role of nitric oxide in the inflamed joint?

OBJECTIVE

To examine the potential consequences of overproduction of nitric oxide (NO) and nitrite (NO(2) (-)) in the inflamed rheumatoid joint.

METHODS

Human articular chondrocytes in culture were exposed to HOCl (hypochlorous acid, a physiologic oxidant formed in increased amounts at sites of chronic inflammation), and assays of cell viability, intracellular ATP and glutathione (GSH), and lactate dehydrogenase (LDH) were performed. HOCl-induced lipid peroxidation and activation of the MAP kinases ERK-1/2, JNK-1/2, and p38 were also measured. The modulatory effects of NO-derived nitrite (NO(2) (-)) and nitrate (NO(3) (-)) on HOCl-mediated chondrocyte toxicity were investigated.

RESULTS

Exposure of human articular chondrocytes to HOCl resulted in a concentration- and time-dependent loss of viability, decrease in ATP and GSH levels, LDH leakage, and cell death. HOCl induced significant lipid peroxidation as well as activation of the MAP kinases ERK-1/2 and p38 but not JNK-1/2. However, the presence of NO(2) (-) but not NO(3) (-) substantially decreased HOCl-dependent cellular toxicity even when NO(2) (-) was added at low (microM) concentrations. In sharp contrast, NO(2) (-) (1 mM) did not inhibit superoxide-, hydroxyl radical-, H(2)O(2)-, or peroxynitrite-mediated cytotoxicity. Furthermore, culture media from cells treated with interleukin-1beta (to generate NO and NO(2) (-)) offered significantly more protection against HOCl-mediated cytotoxicity than culture media from untreated cells.

CONCLUSION

These data suggest that NO(2) (-) accumulation at chronically inflamed sites where both HOCl and NO are overproduced may be cytoprotective against damage induced by HOCl. Accumulation of NO(2) (-) could represent a novel cytoprotective role of NO in inflamed joints. A mechanism for this is suggested.

Development of a novel running buffer for the simultaneous determination of nitrate and nitrite in human serum by capillary zone electrophoresis

In order to improve NO2- peak height and obtain a convenient buffer system for the assay of nitrogen monooxide metabolites, we developed a novel running buffer for the simultaneous determination of nitrite and nitrate in human serum by capillary electrophoresis. The addition of cetyltrimethylammonium chloride to the running buffer resulted in high-speed separation using reverse electroosmotic flow. Highly sensitive determination was also achieved using stacking with 10-fold diluted sample solutions. The samples were injected hydrodynamically for 100 s into a 50 cm x 75 microm I.D. capillary. The separation voltage was 10 kV (negative polarity). UV detection was performed at 214 nm. We obtained complete separation of nitrite and nitrate in deproteinized human serum within 6 min with optimum analytical conditions. Linear calibration curves for nitrite and nitrate for both peak height and peak area were obtained with standard addition method. The limits of detection obtained at a signal-to-noise ratio of 3 for nitrite and nitrate were 4.1 and 2.0 microM, while the values of relative standard deviation of peak height were 2.4 and 2.6%, respectively.

Quantitative capillary zone electrophoresis of inorganic anions

Despite the availability of commercial capillary electrophoresis systems for over ten years, where quantitative analysis is required, capillary zone electrophoresis (CZE) has often failed to replace ion chromatography as the method of choice for a large number of analytes, not least inorganic anions. To investigate the reasons for this apparent failing, a review is presented of work that has been carried out to-date involving the quantitative application of CZE to the determination of inorganic anions in industrial and environmental samples. This review summarizes work both investigating and improving the quantitative aspects of the CZE of inorganic anions. A complete survey of how CZE has been applied to the determination of inorganic anions in real samples is given, including what, if any, analytical performance parameters were investigated and quoted, and if quality assurance data and validation methods were briefly considered, thoroughly investigated or simply ignored.

Iothalamate measured by capillary electrophoresis is a suitable alternative to radiolabeled inulin in renal micropuncture

BACKGROUND

Inulin remains the gold standard for measurements of fluid reabsorption (Jv) and single nephron glomerular filtration rate (SNGFR) in micropuncture experiments. However, the method used to measure cold inulin in nanoliter samples is time-consuming, while the use of radiolabeled inulin is disadvantaged by possible radioactive contamination, disposal of radioactive material and cost of the isotope. It has been reported that non-radiolabeled iothalamate may be a suitable alternative for estimation of whole kidney GFR. The present study tested whether iothalamate can be used to measure Jv in microperfusion and free-flow micropuncture experiments.

METHODS

Superficial loops of Henle (LOH) were perfused from late proximal to early distal tubules with an end-like proximal solution. In the first set of experiments, the perfusate contained both iothalamate (1.9 mmol/L) and 3H-methoxy-inulin (50 microCi. mL(-1)). To test if iothalamate was able to detect changes in Jv, two additional sets of experiments were performed: (1) mannitol (61 mmol/L) was added to the perfusate to partially replace NaCl, a condition known to inhibit Jv; (2) LOH of remnant kidneys were perfused, which in previous experiments we showed to have a higher Jv. Lastly, free-flow micropuncture experiments were performed by infusing iothalamate IV at 18.3 mg. h(-1). Iothalamate analysis in nanoliter samples of renal tubular fluid obtained in vivo was performed by capillary electrophoresis (CE).

RESULTS

In the first set of experiments, liquid scintillation counting of 3H-methoxy-inulin versus iothalamate analysis with CE resulted in almost identical calculated perfusion rates (20.4 +/- 0.6 vs. 20.6 +/- 0.7 nL. min(-1), N = 20) and tubular fluid/perfusate ratios (TF/P; 1.35 +/- 0.04 vs. 1.36 +/- 0.04) and thus also Jv (5.17 +/- 0.50 vs. 5.38 +/- 0.59 nL. min(-1)). In the mannitol experiments, iothalamate measurements showed that the addition of mannitol significantly reduced Jv from 4.98 +/- 0.40 (N = 19) to 0.72 +/- 0.58 nL. min(-1) (N = 33; P < 0.0001). Iothalamate determinations by CE were able to detect a significant increase in Jv in LOH of remnant rats perfused at 40 nL. min(-1)[from to 8.40 +/- 0.73 (N = 20) in sham-operated to 17.8 +/- 2.9 nL. min(-1) (N = 6) in remnant animals; P < 0.0001]. In free flow micropuncture experiments the ratio of tubular fluid to plasma iothalamate (TF/P) along the proximal tubule was 1.62 +/- 0.10 (N = 15).

CONCLUSIONS

These data demonstrate that iothalamate can replace inulin to measure Jv in microperfusion and free-flow micropuncture experiments. Since iothalamate analysis by CE technique is a fast, easy and highly reproducible technique, it may become the gold standard method for the detection of fluid reabsorption in microperfused nephron segments.

Dermal nitrate: an old marker of firearm discharge revisited with capillary electrophoresis

The present work describes a capillary electrophoretic method for nitrite and nitrate determination to be used as a screening tool for investigating the residues of firearm discharge. The use of capillary electrophoresis allowed the rapid determination of nitrite and nitrate, which are major inorganic components of gunshot residues, offering a quantitative and selective alternative to the traditional paraffin test (dermal nitrate test). The method is simpler, cheaper, and faster than the modern approaches to gunshot residue analysis based on the determination of barium, lead and antimony by using flameless absorption spectrometry, inductively coupled plasma-mass spectrometry (ICP-MS), or scanning electron microscopy. The analysis was carried out in a bare fused-silica capillary (75 microm inner diameter) with a 100 mM borate buffer (pH 9.24). The detection was by UV absorption at 214 nm. Separation took place under reversed voltage of 15 kV. Bromide was used as the internal standard. Sensitivity was about 1 mM for both nitrite and nitrate. Reproducibility (intraday and day-to-day) was also good with relative standard deviations (RSDs) < 1.0% for relative migration times and < 4.5% for peak areas in both standard solutions and real matrix. Hair and skin samples from a victim shot in the head were successfully analyzed for the presence of nitrite and nitrate.

Approaches to enhancing the sensitivity of capillary electrophoresis methods for the determination of inorganic and small organic anions

One of the major problems facing the development of capillary electrophoresis (CE) is the relatively high limits of detection when compared to traditional high-performance liquid chromatographic (HPLC) methods. While the use of an alternative detector can offer better sensitivity, a more universal approach is sample preconcentration. Numerous on-line methods have been developed to improve the sensitivity of CE, and are based on electrophoretic principles, chromatographic principles, or a combination of both. This review will discuss all forms of on-line preconcentration methods for CE, with emphasis given to those that have shown particular merit when applied to inorganic and small organic anions.

Nitrite and nitrate measurement in human urine by capillary electrophoresis

Nitrite and nitrate have been widely used as markers for nitric oxide (NO) formation in vivo and represent the major NO oxidation products in biological fluids. In the present study, the use of capillary electrophoresis (CE) in the measurement of nitrite and nitrate in human urine is described. Urine samples were electrophoresed in an extended light path fused-silica capillary (104 cm; 75 microm ID) at an applied negative potential of 30 kV, and UV detection at 214 nm. Using electrokinetic sample injection (-6 kV x 20 s), we found that urine concentration, pH, sodium and chloride interfered with nitrite and nitrate detection. The detection of nitrite and nitrate was decreased when hydrodynamic sample injection was used (30 mbar x 60 s). However, basal levels of urinary nitrite (0.25 +/- 0.05 microM) and nitrate (591 +/- 115 microM) were detected and no interference by variations in urine concentration and pH was noted when hydrodynamic sample injection was used. Thus, hydrodynamic sample injection is convenient for the measurement of urinary nitrite and nitrate and avoids the effect of variations in urine matrices and pH on nitrite and nitrate detection.

Nitrite-derived nitric oxide: a possible mediator of 'acidic-metabolic' vasodilation

The fundamental, yet poorly understood, physiological mechanism known as 'acidic-metabolic' vasodilation, contributes to local blood flow regulation during hypoxia/ischaemia and increased metabolic activity. The vasodilator nitric oxide (NO) has been suggested to be involved in this event. Besides enzymatic production by NO synthases, a novel mechanism for generation of this gas in vivo was recently described. This involves non-enzymatic reduction of inorganic nitrite to NO, a reaction that takes place predominantly during acidic/reducing conditions. We have studied the effects of physiological amounts of nitrite on NO generation and relaxation of rat aorta in vitro in a situation where environmental pH was reduced to levels seen in tissues during hypoxia/ischaemia. The relaxatory effect of nitrite was increased in an acidic buffer solution (pH 6.6) compared with neutral pH; EC50 for nitrite was reduced from 200 to 40 microM. Nitrite-evoked relaxation was effectively prevented by coadministration of an inhibitor of soluble guanylyl cyclase. The relaxation was further potentiated by the addition of ascorbic acid. In parallel, NO was generated from nitrite in a pH dependent manner with even larger amounts seen after addition of ascorbic acid. NO generation from nitrite correlated to the the degree of relaxation of rat aorta. These results illustrate non-enzymatic release of NO from nitrite at physiological concentrations. This may be an important auto-regulated physiological mechanism involved in the regulation of vascular tone during hypoxia/ischaemia.

Modified method for the determination of capillary electrophoresis nitric oxide-correlated nitrate in tissue homogenates

A modified capillary electrophoretic method for the determination of nitric oxide correlated nitrate in several tissue homogenates is described in this study. The method was developed using a running buffer consisting of 200 mM lithium chloride and 10 mM borate buffer at pH 8.5, in a fused-silica column total 82 cm, effective 43 cm length and 75 microm I.D. The signal was measured at 214 nm and controlled current of 200 microA (equivalent to 12.7 kV) was applied in the reversed polarity direction. The sample was injected by vacuum pressure 50 ms (25 nl). In these conditions, bromide as internal standard and nitrate appeared at 7.2 and 8.9 min, respectively. Whole validation procedures were applied and satisfactory results were obtained. The nitrate levels of the tissue homogenates of control and L-NAME applied (heart, brain, kidney, stomach, lung, testis and liver) were monitored by the present method and it was decided that the method is precise and accurate.

Sample stacking of cationic and anionic analytes in capillary electrophoresis

The behavior of charged species along concentration boundaries in capillary zone electrophoresis (CZE) that was first described in detail by Everaerts et al. in 1979 assured the possibility of concentrating charged solutes inside the capillary. The concentration effect is based on the sudden change in analyte electrophoretic velocity brought about by the difference in the magnitude of the electric field. Furthermore, this on-line method could be the needed solution to the problem of low concentration sensitivity in CZE. Sample stacking, which is now its well known name, has then found valuable use in applying CZE in many fields, especially after the in-depth studies performed in the early 90s by Chien and Burgi. This article reviews the theory and methodological developments of sample stacking developed for charged analytes in CZE and also in electrokinetic chromatography. A table conveying the reported applications especially in the biomedical and environmental fields is given. On top of this, other on-line concentration methods for charged species, namely, sample self-stacking, acetonitrile stacking, sweeping, cation selective exhaustive injection-sweeping, and use of a pH junction, are briefly discussed.

Stacking in capillary zone electrophoresis

Due to the short light path of the capillaries, the CE detection limit based on concentration, is far less than that of HPLC and not sufficient for many practical applications. Several methods, based on different electrophoretic maneuvers, can concentrate the sample (stack) easily on the capillary before the separation step of capillary zone electrophoresis (CZE). These methods incorporate different types of discontinuous buffers as the means for invoking different velocities to the same analyte molecules to produce a sharpening of the band (stacking). In CZE, these buffers can be often very simple such as sample dilution or adding to the sample a high concentration of a fast mobility ion. However, in other applications these buffers can be as complicated as those required for isotachophoresis. Stacking can often yield a concentration factor of 5-30-fold, which can improve greatly in CZE the detection limits bringing them very close to those of HPLC. Different methods of stacking, the importance of discontinuous buffers and the different mechanism for concentration on the capillary are reviewed here. As there is a need for more practical applications, there will be more methods devised for stacking in CZE.

Analysis of highly saline samples by capillary zone electrophoresis: enhanced direct UV detection of inorganic anions using on-capillary preconcentration and clean-up techniques

The ability to analyze samples with disparate levels of analyte and matrix ions is among the important benefits defining the practical utility of modern capillary electrophoresis. To compensate for the sensitivity limitations regarding trace-level inorganic anions, a number of on-line approaches that should offer an improved S/N ratio in direct UV detection were examined. The novel use of reversed pre-electrophoresis (at the applied voltage opposite to the separation voltage) made it possible to efficiently remove the most part of high chloride levels from the sample and hence to lower the background signal and to inject increased quantities of fast analyte anions. Specifically, by taking these advantages the sensitivity response of iodide was improved by a factor of 5 over normal CE mode. Using isotachophoretic sample stacking, a two-fold increase in detectability was obtained for moderately mobile anions, nitrate and nitrite, that corresponds to the minimum detectable concentrations close to their natural occurrences in seawater. Furthermore, field-amplified sample injection at increased electrolyte-to-sample matrix concentration ratios enabled the maximum S/N enhancement, with detection limits at the level of 10(-6) M and lower in the presence of > or = 5 x 10(4)-fold molar excess of chloride.

Improvement of capillary zone electrophoresis sensitivity with artificial seawater as the background electrolyte utilizing transient isotachophoresis for the determination of nitrate and nitrate ions in seawater

We describe capillary zone electrophoresis (CZE) with transient isotachophoresis (ITP) for the determination of low concentrations of nitrite and nitrate ions in seawater. Bromide-free artificial seawater was adopted as background electrolyte (BGE) to eliminate the interference of high concentrations of salts in seawater. To reverse the electroosmotic flow (EOF), 3 mM cetyltrimethylammonium chloride (CTAC) was added to the BGE. High concentrations of chlorate were added to sample solutions as the terminating ion to generate the ITP process before the CZE separation. In general, the stacking effect increased with increasing amounts of chlorate injected into the capillary. The limits of detection (LODs) for nitrite and nitrate were 0.063 and 0.033 mg/L when the chlorate concentration was 600 and 200 mM, respectively; these were half of those obtained by CZE without the transient ITP. The LODs were obtained at a signal to noise ratio (S/N) of 3. The relative standard deviations (RSD, n = 10) of the peak areas for these ions were 3.2 and 2.9%. The RSDs of peak heights for these ions were 1.6 and 2.1%. The RSDs of migration times for these ions were 0.67 and 0.46%.

Capillary electrophoresis in clinical and forensic analysis: recent advances and breakthrough to routine applications

This paper is a comprehensive review article on capillary electrophoresis (CE) in clinical and forensic analysis. It is based upon the literature of 1997 and 1998, presents CE examples in major fields of application, and provides an overview of the key achievements encountered, including those associated with the analysis of drugs, serum proteins, hemoglobin variants, and nucleic acids. For CE in clinical and forensic analysis, the past two years witnessed a breakthrough to routine applications. As most coauthors of this review are associated with diagnostic or forensic laboratories now using CE on a routine basis, this review also contains data from routine applications in drug, protein, and DNA analysis. With the first-hand experience of providing analytical service under stringent quality control conditions, aspects of quality assurance, assay specifications for clinical and forensic CE and the pros and cons of this maturing, cost-and pollution-controlled age technology are also discussed.

Coupling of biological sample handling and capillary electrophoresis

The analysis of biological samples (e.g., blood, urine, saliva, tissue homogenates) by capillary electrophoresis (CE) requires efficient sample preparation (i.e., concentration and clean-up) procedures to remove interfering solutes (endogenous/exogenous and/or low-/high-molecular-mass), (in)organic salts and particulate matter. The sample preparation modules can be coupled with CE either off-line (manual), at-line (robotic interface), on-line (coupling via a transfer line) or in-line (complete integration between sample preparation and separation system). Sample preparation systems reported in the literature are based on chromatographic, electrophoretic or membrane-based procedures. The combination of automated sample preparation and CE is especially useful if complex samples have to be analyzed and helps to improve both selectivity and sensitivity. In this review, the different modes of solid-phase (micro-) extraction will be discussed and an overview of the potential of chromatographic, electrophoretic (e.g., isotachophoresis, sample stacking) and membrane-based procedures will be given.

Simultaneous analysis of nitrite, nitrate and the nicotinamide nucleotides by capillary electrophoresis: application to biochemical studies and human extracellular fluids

A simple but rapid capillary electrophoresis method was developed for the measurement of nitrite and nitrate in human extracellular fluids and other aqueous solutions. The capabilities of the method were demonstrated by the measurement of endogenous nitrite and nitrate in plasma and serum samples from healthy volunteers, and serum and synovial fluid samples from rheumatoid arthritis patients. Furthermore, this method was used to simultaneously measure nicotinamide adenine dinucleotide, reduced (NADH), nicotinamide adenine dinucleotide (NAD+), nitrite, and nitrate, when studying the nitrite reductase activity of xanthine oxidase. The stability of nitrite was also investigated and it was found that when whole blood was spiked with nitrite and then processed, the nitrite was more stable in the plasma than in the serum. Our findings may help to explain the variations in basal nitrite concentrations reported in the literature.

Capillary electrophoresis of inorganic anions

This review deals with the separation mechanisms applied to the separation of inorganic anions by capillary electrophoresis (CE) techniques. It covers various CE techniques that are suitable for the separation and/or determination of inorganic anions in various matrices, including capillary zone electrophoresis, micellar electrokinetic chromatography, electrochromatography and capillary isotachophoresis. Detection and sample preparation techniques used in CE separations are also reviewed. An extensive part of this review deals with applications of CE techniques in various fields (environmental, food and plant materials, biological and biomedical, technical materials and industrial processes). Attention is paid to speciations of anions of arsenic, selenium, chromium, phosphorus, sulfur and halogen elements by CE.

Analysis of nitrite and nitrate in biological fluids by capillary electrophoresis

OBJECTIVES

We report a method for determining nitrite and nitrate in biological fluids by capillary electrophoresis.

METHODS

A Waters capillary electrophoresis system was used with a filter for detection at 214 nm. After dilution with distilled water, the sample was loaded hydrostatically onto a 60 cm x 100 microm capillary and electrophoresed at 15 kV in 15 mmol/L sulfate buffer, pH 8.0, containing 2.5% electroosmotic flow modifier.

RESULTS

The retention times for nitrite and nitrate were 3.9 +/- 0.8 and 4.0 +/- 0.8 min, respectively. The detection limit was 10 micromol/L for serum nitrate. The recovery was 93-115% for nitrite and 92-106% for nitrate. The within-day and between-day coefficients of variation were lower than 3.3% and 5.0%, respectively, for two pools with normal (28 micromol/L) and high (87 micromol/L) nitrate concentration. A comparison with the nitrate reductase method gave a correlation coefficient of 0.982.

CONCLUSION

Capillary electrophoresis provides many advantages, namely low cost, small sample and buffer requirements, rapidity, which makes its use particularly suitable for clinical laboratories.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).