Real-time measurement of nitric oxide production in rat brain by the combination of luminol-H2O2 chemiluminescence and microdialysis

A NO-Responsive Ratiometric Fluorescent Nanoprobe for Monitoring Drug-Induced Liver Injury in the Second Near-Infrared Window

Currently, drug-induced liver injury (DILI) has become a huge concern for the majority of modern medicine, whereas the diagnosis of DILI is still in its infancy due to the lack of appropriate methods. Herein, based on the fact that nitric oxide (NO) has been recognized as an early unifying, direct, and vital biomarker for DILI, we rationally designed and developed a NO-responsive ratiometric fluorescent nanoprobe DCNP@MPS@IR NO to quantitatively detect NO and monitor DILI in the second near-infrared (NIR-II) window. In the presence of NO, due to the conversion of IR NO into IR RA and excellent stability of the downconversion nanoparticle (DCNP), DCNP@MPS@IR NO could present a "Turn-On" fluorescence signal at 1050 nm under 808 nm excitation (F_{1050 Em, 808 Ex}) and an "Always-On" fluorescence signal at 1550 nm under 980 nm excitation (F_{1550 Em, 980 Ex}), which led to a "Turn-On" ratiometric fluorescence signal F_{1050 Em, 808 Ex}/F_{1550 Em, 980 Ex}. DCNP@MPS@IR NO was then successfully applied in vitro to selectively detect NO, at a linear concentration range of 0-100 μM with a limit of detection of 0.61 μM. In vivo results revealed that DCNP@MPS@IR was available to quantify NO in acetaminophen (APAP)-induced liver injury, monitor DILI, and screen an antidote for APAP through NIR-II ratiometric fluorescence imaging. We envision that our nanoprobe DCNP@MPS@IR NO might become a really useful biotechnology tool for visualizing and early diagnosis of drug-induced liver injury and revealing the mechanism of drug hepatotoxicity in the clinic in the near future.

Single-Walled Carbon Nanotube-Based Biosensors for Detection of Bronchial Inflammation

Inflammation is a protective mechanism against invading pathogens and tissue damage. However, the inflammatory process is implicated in a wide range of diseases affecting all organs and body systems. Nitric oxide — a multifunctional signaling molecule that plays a critical role in systemic blood pressure homeostasis, prevention of platelet aggregation, antimicrobial resistance, immunoregulation, tumor suppression and as a neurotransmitter — is used as a surrogate marker for inflammation. However, the most commonly used Griess assay is an indirect and expensive method for the determination of nitric oxide concentration. Hence, single-walled carbon nanotube-based biosensors have been explored as real-time, sensitive, selective and safe methods to determine nitric oxide released during the inflammatory process. In this review, we explore current developments in single-walled carbon nanotube-based biosensors for the detection of nitric oxide in exhaled breath as a direct and noninvasive test for detection of bronchial inflammation.

Gas phase microdialysis and chemiluminescence detection: A small, fast, selective, and sensitive method to monitor aqueous nitric oxide

A method using a gas-phase microdialysis probe interfaced with a modified commercially available nitric oxide (NO) detector is shown to selectively measure aqueous NO at low μM levels with high selectivity. The detector measures chemiluminescence resulting from the gas-phase reaction of NO with ozone. The microdialysis probe is small enough (3 mm × 200 μm) to be used in vivo. Because the processes of extraction across the microdialysis membrane and transport from the probe to the detector are both very fast, the response time is shorter than 5 s. The method was verified using two different quantifiable sources of NO: nitrite and methylamine hexamethylene methylamine (MAHMA) NONOates. To demonstrate ruggedness and to show the impact of matrix on NO generation, the method was used to measure NO in a cell culture matrix. The continuous extraction, fast response time, and rugged nature make the method useful for monitoring NO in biological applications. Our results also show that predicting NO concentration for in vitro experiments based on NONOate concentration may be a poor assumption due to the pH dependence of NO formation and the rapid decline in NO concentration.

Nonenzymatic Electrochemical Sensor with Ratiometric Signal Output for Selective Determination of Superoxide Anion in Rat Brain

There is still an urgent need to develop reliable analytical methods of O₂^•- in vivo for deeply elucidating the roles of O₂^•- playing in the brain. Herein, a nonenzymatic electrochemical sensor with ratiometric signal output was developed for an in vivo analysis of O₂^•- in the rat brain. Diphenylphosphonate-2-naphthol ester (ND) was designed and synthesized as a specific recognition molecule for the selective determination of O₂^•-. An anodic peak ascribed to the oxidation of 2-naphthol was generated via the nucleophilic substitution between ND and O₂^•- and was increased with the increasing concentration of O₂^•-. Meanwhile, the inner reference of methylene blue (MB) was co-assembled at the electrode surface to enhance the determination accuracy of O₂^•-. The anodic peak current ratio between 2-naphthol and MB exhibited a good linear relationship with the concentration of O₂^•- from 2 to 200 μM. Because of the stable molecule character of ND and its specific reaction with O₂^•-, the developed electrochemical sensor demonstrated excellent selectivity toward various potential interferences in the brain and good stability even after storage for 7 days. Accordingly, the present electrochemical sensor with high selectivity, high stability, and high accuracy was successfully exploited in monitoring the levels of O₂^•- in the rat brain and that of the diabetic model followed by cerebral ischemia.

Virtual electrochemical nitric oxide analyzer using copper, zinc superoxide dismutase immobilized on carbon nanotubes in polypyrrole matrix

In this work, we have designed and developed a novel and cost effective virtual electrochemical analyzer for the measurement of NO in exhaled breath and from hydrogen peroxide stimulated endothelial cells using home-made potentiostat. Here, data acquisition system (NI MyDAQ) was used to acquire the data from the electrochemical oxidation of NO mediated by copper, zinc superoxide dismutase (Cu,ZnSOD). The electrochemical control programs (graphical user-interface software) were developed using LabVIEW 10.0 to sweep the potential, acquire the current response and process the acquired current signal. The Cu,ZnSOD (SOD1) immobilized on the carbon nanotubes in polypyrrole modified platinum electrode was used as the NO biosensor. The electrochemical behavior of the SOD1 modified electrode exhibited the characteristic quasi-reversible redox peak at the potential, +0.06 V vs. Ag/AgCl. The biological interferences were eliminated by nafion coated SOD1 electrode and then NO was measured selectively. Further, this biosensor showed a wide linear range of response over the concentration of NO from 0.1 μM to 1 mM with a detection limit of 0.1 μM and high sensitivity of 1.1 μA μM(-1). The electroanalytical results obtained here using the developed virtual electrochemical instrument were also compared with the standard cyclic voltammetry instrument and found in agreement with each other.

Multimodality imaging of nitric oxide and nitric oxide synthases

Nitric oxide (NO) and NO synthases (NOSs) are crucial factors in many pathophysiological processes such as inflammation, vascular/neurological function, and many types of cancer. Noninvasive imaging of NO or NOS can provide new insights in understanding these diseases and facilitate the development of novel therapeutic strategies. In this review, we will summarize the current state-of-the-art multimodality imaging in detecting NO and NOSs, including optical (fluorescence, chemiluminescence, and bioluminescence), electron paramagnetic resonance (EPR), magnetic resonance (MR), and positron emission tomography (PET). With continued effort over the last several years, these noninvasive imaging techniques can now reveal the biodistribution of NO or NOS in living subjects with high fidelity which will greatly facilitate scientists/clinicians in the development of new drugs and/or patient management. Lastly, we will also discuss future directions/applications of NO/NOS imaging. Successful development of novel NO/NOS imaging agents with optimal in vivo stability and desirable pharmacokinetics for clinical translation will enable the maximum benefit in patient management.

Sensitive determination of nitric oxide in some rat tissues using polymer monolith microextraction coupled to high-performance liquid chromatography with fluorescence detection

A simple, sensitive, selective, and low-cost method is proposed for rapidly determining nitric oxide (NO) in some rat tissues. Polymer monolith microextraction (PMME) using a poly(methacrylic acid-ethylene glycol dimethacrylate) (MAA-EGDMA) monolithic column was combined with derivatization of NO using 1,3,5,7-tetramethyl-8-(3',4'-diaminophenyl)-difluoroboradiaza-s-indacene (TMDABODIPY), and this was used to analyze the derivatives of NO by high-performance liquid chromatography (HPLC) with fluorescence detection at lambda (ex)/lambda (em) = 498/507 nm. The baseline separation of TMDABODIPY and its NO derivative is performed under simple conditions in which a C(18) column is used and eluted with 50 mmol L(-1) ethanolamine and methanol. The conditions for the extraction of NO derivatives were optimized. The limit of detection of NO was 2 x 10(-12) mol L(-1) (S/N = 3). The linearity range of the method was 9 x 10(-11)-4.5 x 10(-8) mol L(-1). The interday and intraday relative standard deviations were less than 5%. The proposed method was successfully applied to the determination of NO levels in some rat tissue samples including heart, kidney, and liver with recoveries varying from 87.1 to 95.2%.

Specific detection of gaseous NO and 15NO in the headspace from liquid-phase reactions involving NO-generating organic, inorganic, and biochemical samples using a mid-infrared laser

Nitric oxide (NO) is an important biological signaling agent. The specific detection of NO represents a continuing challenge in the field of NO research. Many methods are currently employed for the detection of NO. Here, we report a qualitative but specific detection method for gaseous NO liberated in and from solution taking advantage of its low solubility. Importantly, our mid-infrared laser absorption method does not depend on any chemical derivatization of NO, and is applicable over a wide range of concentrations for both protein work and in organic-inorganic modeling work. We also apply this method to the specific detection of 15NO.

Unexpected effects of nitric oxide synthase inhibitors on extracellular nitrite levels in the hippocampus in vivo

The aim of this study was to determine whether extracellular nitric oxide levels in the hippocampus of freely moving animals were reduced by the administration of nitric oxide synthase (NOS) inhibitors via a microdialysis probe. Our results show that extracellular nitrite levels were increased following the infusion of N-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI), in the case of the latter, the response was biphasic. In contrast, infusion of both inhibitors together resulted in a substantial reduction in nitrite when compared to control. More predictably, the infusion of NMDA elicited an increase in extracellular nitrite levels. This effect was biphasic, the second phase occurring some 3 h after the drug infusion period had ended. When NMDA was infused in the presence of L-NAME, no agonist-induced increase in nitrite production was recorded, in fact nitrite levels were found to decline to below control values. There was no immediate increase in nitrite levels when NMDA was infused in the presence of 7-NI, although this may have been partially obscured by the biphasic effect of the inhibitor. It did appear, however, that the second phase of the NMDA-induced response was attenuated by 7-NI. No NMDA-evoked increase in nitrite was evident when the agonist was infused in the presence of a combination of both inhibitors. We have no clear explanation for the data presented here but suggest that up-regulated activity of particular NOS isoforms might compensate for the inhibition of the other by a mechanism yet to be elucidated. In addition, we propose that caution be exercised when interpreting results from in vivo microdialysis studies where NOS inhibitors are administered directly into the brain via a probe.

Disruption of thiol homeostasis and nitrosative stress in the cerebrospinal fluid of patients with active multiple sclerosis: evidence for a protective role of acetylcarnitine

Recent studies suggest that NO and its reactive derivative peroxynitrite are implicated in the pathogenesis of multiple sclerosis (MS). Patients dying with MS demonstrate increased astrocytic inducible nitric oxide synthase activity, as well as increased levels of iNOS mRNA. Peroxynitrite is a strong oxidant capable of damaging target tissues, particularly the brain, which is known to be endowed with poor antioxidant buffering capacity. Inducible nitric oxide synthase is upregulated in the central nervous system (CNS) of animals with experimental allergic encephalomyelitis (EAE) and in patients with MS. We have recently demonstrated in patients with active MS a significant increase of NOS activity associated with increased nitration of proteins in the cerebrospinal fluid (CSF). Acetylcarnitine is proposed as a therapeutic agent for several neurodegenerative disorders. Accordingly, in the present study, MS patients were treated for 6 months with acetylcarnitine and compared with untreated MS subjects or with patients noninflammatory neurological conditions, taken as controls. Western blot analysis showed in MS patients increased nitrosative stress associated with a significant decrease of reduced glutathione (GSH). Increased levels of oxidized glutathione (GSSG) and nitrosothiols were also observed. Interestingly, treatment of MS patients with acetylcarnitine resulted in decreased CSF levels of NO reactive metabolites and protein nitration, as well as increased content of GSH and GSH/GSSG ratio. Our data sustain the hypothesis that nitrosative stress is a major consequence of NO produced in MS-affected CNS and implicate a possible important role for acetylcarnitine in protecting brain against nitrosative stress, which may underlie the pathogenesis of MS.

Real-time measurement of nitric oxide by luminol-hydrogen peroxide reaction in crystalloid perfused rat heart

The objective of this study was to develop an assay system that allows continuous monitoring of nitric oxide (NO) released from crystalloid perfused hearts. We utilized chemiluminescence reaction between NO and luminol-H(2)O(2) to quantify the NO level in coronary effluent. Isolated rat hearts were subjected to ordinary Langendorff's perfusion, and the right ventricle was cannulated to sample coronary effluent. After equilibration, the coronary flow rate was set constant and the hearts were paced at 300 bpm. Coronary effluent was continuously sampled and mixed with the chemiluminescent probe containing 0.018 mmol/l luminol plus 10 mmol/l H(2)O(2). Chemiluminescence from the mixture of coronary effluent and the probe was continuously measured. NO concentration was calibrated by various concentrations (0.5-400 pmol/l) of standard NO solution. The lower detection limit of NO was 1 pmol/l. Basal NO release from isolated perfused rat heart was 0.41 +/- 0.17 pmol/min/g of heart weight, and that was significantly suppressed by 0.1 mmol/l of L-NAME to 0.18 +/- 0.10 pmol/min/g of heart weight (n = 7). Application of 0.1 and 0.3 micromol/l acetylcholine increased NO level in the coronary effluent, in a concentration-dependent manner, from 6.6 +/- 1.7 in a baseline condition to 16.3 +/- 7.4 and 30.3 +/- 16.1 pmol/l at each peak, respectively. Thrombin at 1 and 10 U/ml also increased NO level from 17.6 +/- 4.3 in control to 35.5 +/- 10.4 and 48.7 +/- 8.7 pmol/l at each peak, respectively (n = 7). Thus, this assay system is applicable to the continuous real-time measurement of NO released from crystalloid perfused hearts, and it may be useful for the study of physiological or pathophysiological role of NO in coronary circulation.

Nitric oxide synthase is present in the cerebrospinal fluid of patients with active multiple sclerosis and is associated with increases in cerebrospinal fluid protein nitrotyrosine and S-nitrosothiols and with changes in glutathione levels

Nitric oxide (NO) is hypothesized to play a role in the immunopathogenesis of multiple sclerosis (MS). Increased levels of NO metabolites have been found in patients with MS. Peroxynitrite, generated by the reaction of NO with superoxide at sites of inflammation, is a strong oxidant capable of damaging tissues and cells. Inducible NO synthase (iNOS) is up-regulated in the CNS of animals with experimental allergic encephalomyelitis (EAE) and in patients with MS. In this study, Western blots of cerebrospinal fluid (CSF) from patients with MS demonstrated the presence of iNOS, which was absent in CSF from control subjects. There was also NOS activity present in both MS and control CSF. Total NOS activity was increased (by 24%) in the CSF from MS patients compared with matched controls. The addition of 0.1 mM ITU (a specific iNOS inhibitor) to the samples did not change the activity of the control samples but decreased the NOS activity in the MS samples to almost control levels. The addition of 1 mM L-NMMA (a nonisoform specific NOS inhibitor), completely inhibited NOS activity in CSF from control and MS subjects. Nitrotyrosine immunostaining of CSF proteins was detectable in controls but was greatly increased in MS samples. There were also significant increases in CSF nitrate + nitrite and oxidant-enhanced luminescence in MS samples compared with controls. Additionally, a significant decrease in reduced glutathione and significant increases in oxidized glutathione and S-nitrosothiols were found in MS samples compared with controls. Parallel changes in NO metabolites were observed in the plasma of MS patients, compared with controls, and accompanied a significant increase of reduced glutathione. These data strongly support a role for nitrosative stress in the pathogenesis of MS and indicate that therapeutic strategies focussed on decreasing production of NO by iNOS and/or scavenging peroxynitrite may be useful in alleviating the neurological impairments that occur during MS relapse.

Measurement of nitric oxide metabolites in brain microdialysates by a sensitive fluorometric high-performance liquid chromatography assay

Nitric oxide (NO), formed from arginine by a specific neuronal NO synthase, is an important neurotransmitter in various regions of the central nervous system. While intracerebral microdialysis is an elegant technique to study local extracellular neurotransmitter concentrations in vivo, NO metabolites (nitrate, nitrite (NO(x))) are difficult to study at high temporal resolution because of low tissue concentrations and small sample volumes. We developed a sensitive fluorometric high-performance liquid chromatography (HPLC)-coupled NO(x) assay adapted for the use in brain microdialysate samples. The assay includes an initial enzymatic step in which nitrate is reduced to nitrite. Nitrite is acidified to N2O3, which reacts with 2,3-diaminonaphthalene to form 1-(H)-naphthotriazole. This reaction product can be readily isolated and quantitated by HPLC with fluorometric detection. The theoretical assay sensitivity is less than 1 nM, but numerous sources of contamination must be eliminated in the sampling and assaying process to reliably monitor brain NO(x) outflow by microdialysis.

Practical methods for detection of nitric oxide

Nitric oxide (NO), which is generated in vivo through conversion of L-arginine to L-citrulline by NO synthase (NOS), mediates many physiological and pathophysiological processes. At least two distinct isoforms of NOS have been identified, constitutive NOS (cNOS) and inducible NOS (iNOS). The cNOS, which is constitutively expressed in endothelial cells and central and peripheral neuronal cells, requires both calcium and calmodulin for its activation. Cells expressing cNOS generally produce small amounts of NO, because of their low levels of cNOS protein. On the other hand, iNOS, which is induced in cells stimulated with endotoxins, produced larger amounts of NO. Because of the short half-life, it is difficult to detect NO in situ directly, especially from cells expressing cNOS. In this review, we discuss practical methods for NO detection, which are useful for the detection of small amounts of NO from cNOS and for the bioimaging of living cells and cultured tissues.