Simultaneous nitric oxide and dehydroascorbic acid imaging by combining diaminofluoresceins and diaminorhodamines

Development of an innovative turn-on fluorescent probe for targeted in-vivo detection of nitric oxide in rat brain extracts as a biomarker for migraine disease

Nitric oxide (NO) is one of the reactive nitrogen species (RNS) that has been proposed to be a key signaling molecule in migraine. Migraine is a neurological disorder that is linked to irregular NO levels, which necessitates precise NO quantification for effective diagnosis and treatment. This work introduces a novel fluorescent probe, 2,3-diaminonaphthelene-1,4-dione (DAND), which was designed and synthesized to selectively detect NO in-vitro and in-vivo as a migraine biomarker. DAND boasts high aqueous solubility, biocompatibility, and facile synthesis, which enable highly selective and sensitive detection of NO under physiological conditions. NO reacts with diamine moieties (recognition sites) of DAND, results in the formation of a highly fluorescent product (DAND-NO) known as 1H-naphtho[2,3-d][1,2,3]triazole-4,9-dione at λem 450 nm. The fluorescence turn-on sensing mechanism operates through an intramolecular charge transfer (ICT) mechanism. To maximize fluorescence signal intensity, parameters including DAND concentration, reaction temperature, reaction time and pH were systematically optimized for sensitive and precise NO determination. The enhanced detection capability (LOD = 0.08 μmol L-1) and high selectivity of the probe make it a promising tool for NO detection in brain tissue homogenates. This demonstrates the potential diagnostic value of the probe for individuals suffering from migraine. Furthermore, this study sheds light on the potential role of zolmitriptan (ZOLM), an antimigraine medication, in modulating NO levels in the brain of rats with nitroglycerin-induced migraine, emphasizing its significant impact on reducing NO levels. The obtained results could have significant implications for understanding how ZOLM affects NO levels and may aid in the development of more targeted and effective migraine treatment strategies.

CeO2-Zn Nanocomposite Induced Superoxide, Autophagy and a Non-Apoptotic Mode of Cell Death in Human Umbilical-Vein-Derived Endothelial (HUVE) Cells

In this study, a nanocomposite of cerium oxide-zinc (CeO₂-Zn; 26 ± 11 nm) based on the antioxidant rare-earth cerium oxide (CeO₂) nanoparticles (NPs) with the modifier zinc (Zn) was synthesized by sintering method and characterized. Its bio-response was examined in human umbilical-vein-derived endothelial (HUVE) cells to get insight into the components of vascular system. While NPs of CeO₂ did not significantly alter cell viability up to a concentration of 200 µg/mL for a 24 h exposure, 154 ± 6 µg/mL of nanocomposite CeO₂-Zn induced 50% cytotoxicity. Mechanism of cytotoxicity occurring due to nanocomposite by its Zn content was compared by choosing NPs of ZnO, possibly the closest nanoparticulate form of Zn. ZnO NPs lead to the induction of higher reactive oxygen species (ROS) (DCF-fluorescence), steeper depletion in antioxidant glutathione (GSH) and a greater loss of mitochondrial membrane potential (MMP) as compared to that induced by CeO₂-Zn nanocomposite. Nanocomposite of CeO₂-Zn, on the other hand, lead to significant higher induction of superoxide radical (O₂^•−, DHE fluorescence), nitric oxide (NO, determined by DAR-2 imaging and Griess reagent) and autophagic vesicles (determined by Lysotracker and monodansylcadeverine probes) as compared to that caused by ZnO NP treatment. Moreover, analysis after triple staining (by annexin V-FITC, PI, and Hoechst) conducted at their respective IC50s revealed an apoptosis mode of cell death due to ZnO NPs, whereas CeO₂-Zn nanocomposite induced a mechanism of cell death that was significantly different from apoptosis. Our findings on advanced biomarkers such as autophagy and mode of cell death suggested the CeO₂-Zn nanocomposite might behave as independent nanostructure from its constituent ones. Since nanocomposites can behave independently of their constituent NPs/elements, by creating nanocomposites, NP versatility can be increased manifold by just manipulating existing NPs. Moreover, data in this study can furnish early mechanistic insight about the potential damage that could occur in the integrity of vascular systems.

Anti-Inflammatory CeO2 Nanoparticles Prevented Cytotoxicity Due to Exogenous Nitric Oxide Donors via Induction Rather Than Inhibition of Superoxide/Nitric Oxide in HUVE Cells

The mechanism behind the cytoprotective potential of cerium oxide nanoparticles (CeO2 NPs) against cytotoxic nitric oxide (NO) donors and H2O2 is still not clear. Synthesized and characterized CeO2 NPs significantly ameliorated the lipopolysaccharide (LPS)-induced cytokines IL-1β and TNF-α. The main goal of this study was to determine the capacities of NPs regarding signaling effects that could have occurred due to reactive oxygen species (ROS) and/or NO, since NP-induced ROS/NO did not lead to toxicity in HUVE cells. Concentrations that induced 50% cell death (i.e., IC50s) of two NO donors (DETA-NO; 1250 ± 110 µM and sodium nitroprusside (SNP); 950 ± 89 µM) along with the IC50 of H2O2 (120 ± 7 µM) were utilized to evaluate cytoprotective potential and its underlying mechanism. We determined total ROS (as a collective marker of hydrogen peroxide, superoxide radical (O2•-), hydroxyl radical, etc.) by DCFH-DA and used a O2•- specific probe DHE to decipher prominent ROS. The findings revealed that signaling effects mediated mainly by O2•- and/or NO are responsible for the amelioration of toxicity by CeO2 NPs at 100 µg/mL. The unaltered effect on mitochondrial membrane potential (MMP) due to NP exposure and, again, CeO2 NPs-mediated recovery in the loss of MMP due to exogenous NO donors and H2O2 suggested that NP-mediated O2•- production might be extra-mitochondrial. Data on activated glutathione reductase (GR) and unaffected glutathione peroxidase (GPx) activities partially explain the mechanism behind the NP-induced gain in GSH and persistent cytoplasmic ROS. The promoted antioxidant capacity due to non-cytotoxic ROS and/or NO production, rather than inhibition, by CeO2 NP treatment may allow cells to develop the capacity to tolerate exogenously induced toxicity.

Pt-Coated Au Nanoparticle Toxicity Is Preferentially Triggered Via Mitochondrial Nitric Oxide/Reactive Oxygen Species in Human Liver Cancer (HepG2) Cells

Reactive nitrogen species (RNS) that are formed from the reaction of versatile nitric oxide (NO) with reactive oxygen species (ROS) have been less explored in potential cancer therapy. This may be partly due to the fewer available agents that could induce NO in cells. Here, we report platinum-coated gold nanoparticles (Pt-coated Au NPs; 27 ± 20 nm) as a strong inducer of NO (assessed by live-cell imaging under NO-specific DAR-1 probe labeling and indirectly using a Griess reagent) in human liver carcinoma (HepG2) cells. In addition to NO, this study found a critical role of ROS from mitochondrial sources in the mechanism of toxicity caused by Pt-coated Au NPs. Cotreatment with a thiol-replenishing general antioxidant NAC (N-acetyl cysteine) led to significant amelioration of oxidative stress against NP-induced toxicity. However, NAC did not exhibit as much ameliorative potential against NP-induced oxidative stress as the superoxide radical (O2•-)-scavenging mitochondrial specific antioxidant mito-TEMPO did. The higher protective potential of mito-TEMPO in comparison to NAC reveals mitochondrial ROS as an active mediator of NP-induced toxicity in HepG2 cells. Moreover, the relatively unaltered NP-induced NO concentration under cotreatment of GSH modulators NAC and buthionine sulfoximine (BSO) suggested that NO production due to NP treatment is rather independent of the cellular thiols at least in HepG2 cells. Moreover, toxicity potentiation by exogenous H2O2 again suggested a more direct involvement of ROS/RNS in comparison to the less potentiation of toxicity due to GSH-exhausting BSO. A steeper amelioration in NP-induced NO and ROS and, consequently, cytotoxicity by mito-TEMPO in comparison to NAC reveal a pronounced role of NO and ROS via the mitochondrial pathway in the toxicity of Pt-coated Au NPs in HepG2 cells.

Dual-locked spectroscopic probes for sensing and therapy

Optical imaging probes allow us to detect and uncover the physiological and pathological functions of an analyte of interest at the molecular level in a non-invasive, longitudinal manner. By virtue of simplicity, low cost, high sensitivity, adaptation to automated analysis, capacity for spatially resolved imaging and diverse signal output modes, optical imaging probes have been widely applied in biology, physiology, pharmacology and medicine. To build a reliable and practically/clinically relevant probe, the design process often encompasses multidisciplinary themes, including chemistry, biology and medicine. Within the repertoire of probes, dual-locked systems are particularly interesting as a result of their ability to offer enhanced specificity and multiplex detection. In addition, chemiluminescence is a low-background, excitation-free optical modality and, thus, can be integrated into dual-locked systems, permitting crosstalk-free fluorescent and chemiluminescent detection of two distinct biomarkers. For many researchers, these dual-locked systems remain a 'black box'. Therefore, this Review aims to offer a 'beginner's guide' to such dual-locked systems, providing simple explanations on how they work, what they can do and where they have been applied, in order to help readers develop a deeper understanding of this rich area of research.

Aromatic secondary amine-functionalized fluorescent NO probes: improved detection sensitivity for NO and potential applications in cancer immunotherapy studies

Tumor-associated macrophages (TAMs), constituting up to 50% of the solid tumor mass and commonly having a pro-tumoral M2 phenotype, are closely associated with decreased survival in patients. Based on the highly dynamic properties of macrophages, in recent years the repolarization of TAMs from pro-tumoral M2 phenotype to anti-tumoral M1 phenotype by various strategies has emerged as a promising cancer immunotherapy approach for improving cancer therapy. Herein, we present an aromatic secondary amine-functionalized Bodipy dye 1 and its mitochondria-targetable derivative Mito1 as fluorescent NO probes for discriminating M1 macrophages from M2 macrophages in terms of their difference in inducible NO synthase (iNOS) levels. The two probes possess the unique ability to simultaneously respond to two secondary oxides of NO, i.e., N2O3 and ONOO-, thus being more sensitive and reliable for reflecting intracellular NO than most of the existing fluorescent NO probes that usually respond to N2O3 only. With 1 as a representative, the discrimination between M1 and M2 macrophages, evaluation of the repolarization of TAMs from pro-tumoral M2 phenotype to anti-tumoral M1 phenotype, and visualization of NO communication during the immune-mediated phagocytosis of cancer cells by M1 macrophages have been realized. These results indicate that our probes should hold great potential for imaging applications in cancer immunotherapy studies and relevant anti-cancer drug screening.

Design of a Pyrene Scaffold Multifunctional Material: Real-Time Turn-On Chemosensor for Nitric Oxide, AIEE Behavior, and Detection of TNP Explosive

A dual-emission pyrene-based new fluorescent probe (N-(4-nitro-phenyl)-N'-pyren-1-ylmethyl-ene-ethane-1,2-diamine (PyDA-NP)) displays green fluorescence for nitric oxide (NO) sensing, whereas it exhibits blue emission in the aggregated state. The mechanism of nitric oxide (NO/NO+) sensing is based on N-nitrosation of aromatic secondary amine, which was not interfered by reactive oxygen species and reactive nitrogen species. The aggregation-induced enhancement of emission (AIEE) behaviors of the PyDA-NP could be attributed to the restriction of intramolecular rotation and vibration, resulting in rigidity enhancement of the molecules. The AIEE behavior of the probe was well established from fluorescence, dynamic light scattering, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, optical fluorescence microscopy, and time-resolved photoluminescence studies. In a H2O/CH3CN binary mixture (8:2 v/v), the probe showed maximum aggregation with extensive (833-fold) increases in fluorescence intensity and high quantum yield (0.79). The aggregated state of the probe was further applied for the detection of nitroexplosives. It displayed efficient sensing of 2,4,6-trinitrophenol (TNP), corroborating mainly the charge-transfer process from pyrene to a highly electron-deficient TNP moiety. Furthermore, for the on-site practical application of the proposed analytical system, a contact-mode analysis was performed.

A rhodamine-based fast and selective fluorescent probe for monitoring exogenous and endogenous nitric oxide in live cells

A sensitive and selective fluorescent probe for fast detection of nitric oxide was synthesized by grafting a NO-trapper o-phenylenediamine onto a rhodamine fluorophore.

Nitric oxide activatable photosensitizer accompanying extremely elevated two-photon absorption for efficient fluorescence imaging and photodynamic therapy

A nitric oxide (NO) activatable photosensitizer was constructed for efficient fluorescence imaging and photodynamic therapy.

Elevated nitric oxide (NO) levels perform an important pathological role in various inflammatory diseases. Developing NO-activatable theranostic materials with a two-photon excitation (TPE) feature is highly promising for precision imaging and therapy, but constructing such materials is still a tremendous challenge. Here, we present the first example of a NO-activatable fluorescent photosensitizer (DBB-NO) accompanying extremely NO-elevated two-photon absorption (TPA) for efficient fluorescence imaging and photodynamic therapy (PDT). Upon responding to NO, DBB-NO shows not only a remarkably enhanced fluorescence quantum yield (Φ_F, 0.17% vs. 9.3%) and singlet oxygen quantum yield (Φ_Δ, 1.2% vs. 82%) but also an extremely elevated TPA cross-section (δ, 270 vs. 2800 GM). Simultaneous enhancement of Φ_Δ, Φ_F and δ allows unprecedented two-photon fluorescence brightness (δ × Φ_F = 260.4 GM) and two-photon PDT (TP-PDT) efficiency (δ × Φ_Δ = 2296 GM) which precedes the value for a commercial two-photon photosensitizer by two orders of magnitude. With these merits, the proof-of-concept applications of NO-activatable two-photon fluorescence imaging and TP-PDT in activated macrophages (in which NO is overproduced) were readily realized. This work may open up many opportunities for constructing two-photon theranostic materials with other pathological condition-activatable features for precise theranostics.

Selective and sensitive visualization of endogenous nitric oxide in living cells and animals by a Si-rhodamine deoxylactam-based near-infrared fluorescent probe

A Si-rhodamine deoxylactam-based near-infrared fluorescent probe has been successfully developed for the imaging of endogenous NO in living cells and mouse models.

Nitric oxide (NO) is a fundamental signaling molecule that regulates virtually every critical cellular function, and it is also a potent mediator of cellular damage in a wide range of conditions mainly via its secondary metabolite peroxynitrite (ONOO^–). In this work, we present an o-phenylenediamine (OPD)-locked Si-rhodamine deoxylactam, i.e.deOxy-DALSiR, as a near-infrared fluorescent probe for the selective and sensitive detection of NO in living cells and bodies. Not only could the probe overcome the limitations suffered by widely used and commercialized OPD-type fluorescent NO probes, such as the possible interferences by dehydroascorbic acid/ascorbic acid/methylglyoxal (DHA/AA/MGO), pH-sensitive fluorescence output, and short excitation and emission wavelengths, but it can also avoid serious interference from cysteine (Cys) found in the rhodamine lactam-based fluorescent NO probes developed later. What’s more, the probe is fairly sensitive for NO, as evidenced by its rapid fluorescence response rate (within seconds), huge fluorescence off–on ratio (6300-fold), and ultra-low detection limit (0.12 nM). Its effectiveness and practicability have been demonstrated by the successful imaging of endogenous NO in RAW 264.7 macrophages, pancreatic β-cells, and endothelial EA.hy926 cells, as well as in inflamed and diabetic mouse models.

An N-nitrosation reactivity-based two-photon fluorescent probe for the specific in situ detection of nitric oxide

In situ fluorescence imaging of nitric oxide (NO) is a powerful tool for studying the critical roles of NO in biological events. However, the selective imaging of NO is still a challenge because most currently available fluorescent probes rely on the o-phenylenediamine (OPD) recognition site, which reacts with both NO and some abundant reactive carbonyl species (RCS) (such as dehydroascorbic acid and methylglyoxal) and some reactive oxygen/nitrogen species (ROS/RNS). To address this problem, a new fluorescent probe, NCNO, based on the N-nitrosation of aromatic secondary amine was designed to bypass the RCS, ROS, and RNS interference. As was expected, the probe NCNO could recognize NO with pronounced selectivity and sensitivity among ROS, RNS, and RCS. The probe was validated by detecting NO in live cells and deep tissues owing to its two-photon excitation and red-light emission. It was, hence, applied to monitor NO in ischemia reperfusion injury (IRI) in mice kidneys by two-photon microscopy for the first time, and the results vividly revealed the profile of NO generation in situ during the renal IRI process.

Aromatic primary monoamine-based fast-response and highly specific fluorescent probes for imaging the biological signaling molecule nitric oxide in living cells and organisms

Two fast-response and highly specific NO fluorescent probes were developed, based on the reductive deamination reaction of p-methoxyaniline with NO in aerobic conditions.

Fluorescent probes for real-time measurement of nitric oxide in living cells

Nitric oxide (NO) is an important signaling molecule in biology. Both NO excess and insufficiency have been implicated in numerous physiological and pathological conditions. In order to study the diverse biological roles of NO in cells and tissues, many techniques have been developed for assaying NO. Recently, new generations of fluorescent probes have become indispensible tools for the study of NO biology because of their sensitivity, selectivity, spatiotemporal resolution, and experimental feasibility. Rational application of these probes in the study requires the understanding of the molecular mechanism that the probes are involved in. In this review, we will present an arsenal of fluorescent probes used to detect NO in living cells and animal tissues. We will also discuss the molecular mechanisms, actualities and prospects of fluorescent probes in detecting NO in cell biology.

Fluorescence turn-on for the highly selective detection of nitric oxide in vitro and in living cells

A water-soluble, biocompatible, small molecular fluorescent turn-on probe was developed for the highly selective and sensitive detection of NO in vitro and in living cells.

Fast-response and highly selective fluorescent probes for biological signaling molecule NO based on N-nitrosation of electron-rich aromatic secondary amines

Nitric oxide (NO) is a ubiquitous biological messenger molecule, and plays the active roles in the regulation of various physiological processes. Although numerous NO fluorescent probes have also been successfully developed in the past ten years, it still remains challenging to increase the response rate for NO while having the high selectivity and sensitivity. In this work, a simple N-nitrosation reaction of the electron-rich aromatic secondary amine with NO under aerobic condition has been utilized for the first time to construct fluorescent probe for NO. The resulting probe 1, containing a N-benzyl-4-hydroxyaniline moiety as reaction group and a BODIPY dye as fluorescence reporter, could detect NO with the fast fluorescence off-on response (within seconds), high sensitivity (nM level), and excellent selectivity over various reactive oxygen species (ROS) as well as dehydroascorbic acid (DHA), ascorbic acid (AA), and methylglyoxal (MGO). Even in the presence of glutathione (GSH, a high reactive biothiol for NO), the probe still works well for NO. Further, a mitochondria-targetable probe 2 was exploited by introducing a targeted triphenylphosphonium cation into probe 1 scaffold. It's excellent NO sensing performance as well as its ability to specifically target mitochondria and image NO there have been nicely demonstrated. With the two probes, the basal and stimulation-induced NO in RAW264.7 murine macrophages as well as the endogenous NO in endothelial cells after oxygen-glucose deprivation (OGD) have been successfully visualized.

Characterisation and comparison of temporal release profiles of nitric oxide generating donors

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Nitric oxide release profiles were characterised for commonly used donors.

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Released NO differs greatly between donors and depends on storage conditions.

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High release donors (NOC-5, PAPA NONOate) decay quickly.

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SNP and GSNO show greater stability releasing consistent lower NO levels.

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This comprehensive characterisation provides knowledge to define NO concentrations released in vitro.

Background

Nitric oxide (NO) is a vital signalling molecule in a variety of tissues including the neuronal, vascular and reproductive system. However, its high diffusibility and inactivation make characterisation of nitrergic signalling difficult. The use of NO donors is essential to characterise downstream signalling pathways but knowledge of donor release capacities is lacking, thus making comparisons of donor responses difficult.

New method

This study characterises NO profiles of commonly used NO donors. Donors were stored under defined conditions and temporal release profiles detected to allow determination of released NO concentrations.

Results

Using NO-sensitive microsensors we assessed release profiles of NO donors following different storage times and conditions. We found that donors such as NOC-5 and PAPA-NONOate decayed substantially within days, whereas SNP and GSNO showed greater stability releasing consistent levels of NO over days. In all donors tested, the amount of released NO differs between frozen and unfrozen stocks.

Comparison with existing method(s)

Fluorescent and amperometric approaches to measure NO concentrations yield a wide range of levels. However, due to a lack of characterisation of the release profiles, inconsistent effects on NO signalling have been widely documented. Our systematic assessment of release profiles of a range of NO donors therefore provides new essential data allowing for improved and defined investigations of nitrergic signalling.

Conclusions

This is the first systematic comparison of temporal release profiles of different NO donors allowing researchers to compare conditions across different studies and the use of defined NO levels by choosing specific donors and concentrations.

A mitochondria-targetable fluorescent probe for dual-channel NO imaging assisted by intracellular cysteine and glutathione

A mitochondria-specific fluorescent probe for NO (1) was synthesized by the direct conjugation of a pyronin dye with one of the amino groups of o-phenylenediamino (OPD). The probe could selectively detect NO over dehydroascorbic acid (DHA), ascorbic acid (AA), and methylglyoxal (MGO) as well as the reactive oxygen/nitrogen species (ROS/RNS) with the significant off-on response due to the production of a red-emission triazole 2. In the presence of cysteine/glutathione (Cys/GSH), 2 could be further transformed into a green-emission aminopyronin 4 and a red-emission thiopyronin 5, respectively. Assisted by intracellular Cys and GSH, the probe demonstrated its potential to monitor mitochondrial NO in a dual-channel mode.

A specific fluorescent probe for NO based on a new NO-binding group

A highly selective fluorescent probe for NO was exploited based on a specific NO-binding group, 2-amino-3′-dimethylaminobiphenyl.

Nitric oxide generated by the rice blast fungus Magnaporthe oryzae drives plant infection

Plant-derived nitric oxide (NO) triggers defence, priming the onset of the hypersensitive response and restricting pathogen ingress during incompatibility. However, little is known about the role of pathogen-produced NO during pre-infection development and infection. We sought evidence for NO production by the rice blast fungus during early infection. NO production was measured using fluorescence of DAR-4M and the role of NO assessed using NO scavengers. The synthesis of NO was investigated by targeted knockout of genes potentially involved in NO synthesis, including nitric oxide synthase-like genes (NOL2 and NOL3) and nitrate (NIA1) and nitrite reductase (NII1), generating single and double Δnia1Δnii1, Δnia1Δnol3, and Δnol2Δnol3 mutants. We demonstrate that Magnaporthe oryzae generates NO during germination and in early development. Removal of NO delays germling development and reduces disease lesion numbers. NO is not generated by the candidate proteins tested, nor by other arginine-dependent NO systems, by polyamine oxidase activity or non-enzymatically by low pH. Furthermore, we show that, while NIA1 and NII1 are essential for nitrate assimilation, NIA1, NII1, NOL2 and NOL3 are all dispensable for pathogenicity. Development of M. oryzae and initiation of infection are critically dependent on fungal NO synthesis, but its mode of generation remains obscure.

Nitric oxide turn-on fluorescent probe based on deamination of aromatic primary monoamines

The stable, water-soluble, and nonfluorescent FA-OMe can sense nitric oxide (NO) and form the intensely fluorescent product dA-FA-OMe via reductive deamination of the aromatic primary amine. The reaction is accompanied by a notable increase of the fluorescent quantum yield from 1.5 to 88.8%. The deamination mechanism of FA-OMe with NO was proposed in this study. The turn-on fluorescence signals were performed by suppression of photoinduced electron transfer (PeT), which was demonstrated by density functional theory (DFT) calculations of the components forming FA-OMe and dA-FA-OMe. Furthermore, FA-OMe showed water solubility and good stability at physiological pHs. Moreover, the selectivity study indicated that FA-OMe had high specificity for NO over other reactive oxygen/nitrogen species. In an endogenously generated NO detection study, increasing the incubation time of FA-OMe with lipopolysaccharide (LPS) pretreated Raw 264.7 murine macrophages could cause an enhanced fluorescence intensity image. In addition, a diffusion/localization cell imaging study showed that FA-OMe could be trapped in Raw 264.7 cells. These cell imaging results demonstrated that FA-OMe could be used as a turn-on fluorescent sensor for the detection of endogenously generated NO.

Profiling metabolites and peptides in single cells

The intracellular levels and spatial localizations of metabolites and peptides reflect the state of a cell and its relationship to its surrounding environment. Moreover, the amounts and dynamics of metabolites and peptides are indicative of normal or pathological cellular conditions. Here we highlight established and evolving strategies for characterizing the metabolome and peptidome of single cells. Focused studies of the chemical composition of individual cells and functionally defined groups of cells promise to provide a greater understanding of cell fate, function and homeostatic balance. Single-cell bioanalytical microanalysis has also become increasingly valuable for examining cellular heterogeneity, particularly in the fields of neuroscience, stem cell biology and developmental biology.

PRODUCTION OF NITRIC OXIDE WITHIN THE APLYSIA CALIFORNICA NERVOUS SYSTEM

Nitric oxide (NO), an intercellular signaling molecule, helps coordinate neuronal network activity. Here we examine NO generation in the Aplysia central nervous system using 4,5-diaminofluorescein diacetate (DAF-2 DA), a fluorescent reagent that forms 4,5-diaminofluorescein triazole (DAF-2T) upon reaction with NO. Recognizing that other fluorescence products are formed within the biochemically complex intracellular environment, we validate the observed fluorescence as being from DAF-2T; using both capillary electrophoresis and mass spectrometry we confirm that DAF-2T is formed from tissues and cells exposed to DAF-2 DA. We observe three distinct subcellular distributions of fluorescence in neurons exposed to DAF-2 DA. The first shows uniform fluorescence inside the cell, with these cells being among previously confirmed NOS-positive regions in the Aplysia cerebral ganglion. The second, seen inside buccal neurons, exhibits point sources of fluorescence, 1.5 ± 0.7 µm in diameter. Interestingly, the number of fluorescence puncta increases when the tissue is preincubated with the NOS substrate L-arginine, and they disappear when cells are preexposed to the NOS inhibitor L-NAME, demonstrating that the fluorescence is connected to NOS-dependent NO production. The third distribution type, seen in the R2 neuron, also exhibits fluorescent puncta, but only on the cell surface. Fluorescence is also observed in the terminals of cultured bag cell neurons loaded with DAF-2 DA. Surprisingly, fluorescence at the R2 surface and bag cell neuron terminals is not modulated by L-arginine or L-NAME, suggesting it has a source distinct from the buccal and cerebral ganglion DAF 2T-positive tissues.

Review of recent advances in analytical techniques for the determination of neurotransmitters

Methods and advances for monitoring neurotransmitters in vivo or for tissue analysis of neurotransmitters over the last five years are reviewed. The review is organized primarily by neurotransmitter type. Transmitter and related compounds may be monitored by either in vivo sampling coupled to analytical methods or implanted sensors. Sampling is primarily performed using microdialysis, but low-flow push-pull perfusion may offer advantages of spatial resolution while minimizing the tissue disruption associated with higher flow rates. Analytical techniques coupled to these sampling methods include liquid chromatography, capillary electrophoresis, enzyme assays, sensors, and mass spectrometry. Methods for the detection of amino acid, monoamine, neuropeptide, acetylcholine, nucleoside, and soluble gas neurotransmitters have been developed and improved upon. Advances in the speed and sensitivity of these methods have enabled improvements in temporal resolution and increased the number of compounds detectable. Similar advances have enabled improved detection at tissue samples, with a substantial emphasis on single cell and other small samples. Sensors provide excellent temporal and spatial resolution for in vivo monitoring. Advances in application to catecholamines, indoleamines, and amino acids have been prominent. Improvements in stability, sensitivity, and selectivity of the sensors have been of paramount interest.

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.

A cellular model for screening neuronal nitric oxide synthase inhibitors

Nitric oxide synthase (NOS) inhibitors are potential drug candidates because it has been well demonstrated that excessive production of nitric oxide critically contributes to a range of diseases. Most inhibitors have been screened in vitro using recombinant enzymes, leading to the discovery of a variety of potent compounds. To make inhibition studies more physiologically relevant and bridge the gap between the in vitro assay and in vivo studies, we report here a cellular model for screening NOS inhibitors. Stable transformants were generated by overexpressing rat neuronal NOS in HEK 293T cells. The enzyme was activated by introducing calcium ions into cells, and its activity was assayed by determining the amount of nitrite that was formed in culture medium using the Griess reagent. We tested a few NOS inhibitors with this assay and found that the method is sensitive, versatile, and easy to use. The cell-based assay provides more information than in vitro assays regarding the bioavailability of NOS inhibitors, and it is suitable for high-throughput screening.