Measuring nitric oxide in single neurons by capillary electrophoresis with laser-induced fluorescence: use of ascorbate oxidase in diaminofluorescein measurements

Bone Formation in Zebrafish: The Significance of DAF-FM DA Staining for Nitric Oxide Detection

DAF-FM DA is widely used as a live staining compound to show the presence of nitric oxide (NO) in cells. Applying this stain to live zebrafish embryos is known to indicate early centers of bone formation, but the precise (cellular) location of the signal has hitherto not been revealed. Using sections of zebrafish embryos live-stained with DAF-FM DA, we could confirm that the fluorescent signals were predominantly located in areas of ongoing bone formation. Signals were observed in the bone and tooth matrix, in the notochord sheath, as well as in the bulbus arteriosus. Surprisingly, however, they were exclusively extracellular, even after very short staining times. Von Kossa and Alizarin red S staining to reveal mineral deposits showed that DAF-FM DA stains both the mineralized and non-mineralized bone matrix (osteoid), excluding that DAF-FM DA binds non-specifically to calcified structures. The importance of NO in bone formation by osteoblasts is nevertheless undisputed, as shown by the absence of bone structures after the inhibition of NOS enzymes that catalyze the formation of NO. In conclusion, in zebrafish skeletal biology, DAF-FM DA is appropriate to reveal bone formation in vivo, independent of mineralization of the bone matrix, but it does not demonstrate intracellular NO.

Headspace Solid-Phase Microextraction Following Chemical Vapor Generation for Ultrasensitive, Matrix Effect-Free Detection of Nitrite by Microplasma Optical Emission Spectrometry

A new chemical vapor generation method coupled with headspace solid-phase microextraction miniaturized point discharge optical emission spectrometry (HS-SPME-μPD-OES) for the sensitive and matrix effect-free detection of nitrite in complex samples is described. In an acidic medium, the volatile cyclohexene was generated from cyclamate in the presence of nitrite, which was volatilized to the headspace of the container, efficiently separated, and preconcentrated by HS-SPME. Consequently, the SPME fiber was transferred to a laboratory-constructed thermal desorption chamber wherein the cyclohexene was thermally desorbed and swept into μPD-OES for its sensitive quantification via monitoring the carbon atomic emission line at 193.0 nm. As a result, the quantification of nitrite was accomplished through the determination of cyclohexene. The application of HS-SPME as a sampling technique not only simplifies the experimental setup of μPD-OES but it also preconcentrates and separates cyclohexene from N₂ and sample matrices, thus eliminating the interference from water vapor and N₂ and significantly improving the analytical performance on the determination of nitrite. Under the optimum experimental conditions, a limit of detection of 0.1 μg L^-1 was obtained, which is much better than that obtained by conventional methods. The precision, expressed as relative standard deviation, was better than 3.0% at a concentration of 10 μg L^-1. The proposed method provides several advantages of portability, simplicity, high sensitivity, and low energy consumption and eliminates expensive instruments and matrix interference, thus retaining a promising potential for the rapid, sensitive, and field analysis of nitrite in various samples.

Measuring stimulation and inhibition of intracellular nitric oxide production in SIM-A9 microglia using microfluidic single-cell analysis

Chronic neuroinflammation has long been considered to be a central factor in accelerating the progression of neurodegenerative diseases such as Alzheimer's diseases, Parkinson's disease and chronic traumatic encephalopathy. Under pathological conditions microglia produce inflammatory signaling molecules, such as nitric oxide (NO), that can damage DNA and proteins and ultimately induce neuronal apoptosis. One strategy for treating neurodegenerative diseases is to specifically target NO production through inhibition of inducible nitric oxide synthase (iNOS). However, accurately measuring changes in microglial NO production in response to potential therapeutics is challenging due to NO's short half-life and microglial heterogeneity. In this paper we report the application of a microfluidic device for the high-throughput measurement of intracellular NO in SIM-A9 microglial cells. NO production was measured in response to treatment with lipopolysaccharides (LPS) and interferon gamma (IFN-γ) with and without a potent iNOS inhibitor (1400 W dihydrochloride). Cells were labeled with a fluorogenic NO probe, 4-amino-5-methylamino-2',7'-difluorofluoescein diacetate (DAF-FM DA), and 6-carboxyfluorescein diacetate (6-CFDA) as an internal standard. Separation and quantitation of intracellular NO was achieved using microchip electrophoresis and laser induced fluorescence detection (LIF). Statistical analysis suggests that the populations fit a lognormal distribution and are better represented by their geometric mean values. Comparison of the geometric means indicated a 1.6-fold increase in NO production between untreated and stimulated cells and a decrease by a factor of approximately 0.5 comparing stimulated and inhibited cells. Additionally, we report experimental data demonstrating the improvement in the sensitivity of our integrated optical fiber-based detection system through the use of refractive index matching gel.

Nitric oxide detection methods in vitro and in vivo

Initially being considered as an environmental pollutant, nitric oxide has gained the momentum of research since its discovery as endothelial derived growth factor in 1987. Extensive researches have revealed the various pathological and physiological roles of nitric oxide such as inflammation, vascular and neurological regulation functions. Hence, the development of methods for quantifying nitric oxide concentration and its metabolites will be beneficial to well know about its biological functions and effects. This review summaries various methods for in vitro and in vivo nitric oxide detection, and introduces their merits and demerits.

Optimization of a microchip electrophoresis method with electrochemical detection for the determination of nitrite in macrophage cells as an indicator of nitric oxide production

Nitric oxide (NO) is involved in many biological functions, including blood pressure regulation, the immune response, and neurotransmission. However, excess production of NO can lead to the generation of reactive nitrogen species and nitrosative stress and has been linked to several neurodegenerative diseases and cardiovascular disorders. Because NO is short-lived and generally difficult to detect, its primary stable degradation product, nitrite, is frequently monitored in its place. In this paper, an improved method using microchip electrophoresis with electrochemical detection (ME-EC) was developed for the separation and detection of nitrite in cell lysates. A separation of nitrite from several electroactive cell constituents and interferences was optimized, and the effect of sample and buffer conductivity on peak efficiency was explored. It was found that the addition of 10 mM NaCl to the run buffer caused stacking of the nitrite peak and improved limits of detection. A platinum black working electrode was also evaluated for the detection of nitrite and other electroactive cellular species after electrophoretic separation. The use of a modified platinum working electrode resulted in 2.5-, 1.7-, and 7.2-fold signal enhancement for nitrite, ascorbic acid, and hydrogen peroxide, respectively, and increased the sensitivity of the method for nitrite twofold. The optimized ME-EC method was used to compare nitrite production by native and lipopolysaccharide-stimulated RAW 264.7 macrophage cells.

Self-Assembly Controls Reactivity with Nitric Oxide: Implications for Fluorescence Sensing

Three molecules containing the fluorophore 4-amino-1,8-naphthalimide (ANI) and showing different tendencies to self-assembly in aqueous environment have been prepared and fully characterized. The fluorescence emissions of two of these compounds in aqueous solutions are efficiently quenched in the presence of nitric oxide (NO) in aerated medium. Nuclear magnetic resonance and mass spectrometry techniques indicate that NO/O2 induces deamination of the ANI fluorophore, resulting in nonemissive 1,8-naphtalimide derivatives. It is found that the reactivity toward NO/O2 is regulated by the different aggregation modes presented by the molecules in aqueous medium. In this way, the molecules displaying fluorescence response toward NO/O2 are those with weak self-association properties whereas the compound with a high hydrophobic character (self-assembling into large nanoparticles) is insensitive to this species. Ultimately, the results described here could not only set the basis for the design of fluorescent bioprobes for NO/O2 based on ANI derivatives or other monoamino compounds but also could raise awareness about the importance of supramolecular interactions for the design of chemosensors.

Microchip electrophoresis with laser-induced fluorescence detection for the determination of the ratio of nitric oxide to superoxide production in macrophages during inflammation

It is well known that excessive production of reactive oxygen and nitrogen species is linked to the development of oxidative stress-driven disorders. In particular, nitric oxide (NO) and superoxide (O₂^•-) play critical roles in many physiological and pathological processes. This article reports the use of 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate and MitoSOX Red in conjunction with microchip electrophoresis and laser-induced fluorescence detection for the simultaneous detection of NO and O₂^•- in RAW 264.7 macrophage cell lysates following different stimulation procedures. Cell stimulations were performed in the presence and absence of cytosolic (diethyldithiocarbamate) and mitochondrial (2-methoxyestradiol) superoxide dismutase (SOD) inhibitors. The NO/O₂^•- ratios in macrophage cell lysates under physiological and proinflammatory conditions were determined. The NO/O₂^•- ratios were 0.60 ± 0.07 for unstimulated cells pretreated with SOD inhibitors, 1.08 ± 0.06 for unstimulated cells in the absence of SOD inhibitors, and 3.14 ± 0.13 for stimulated cells. The effect of carnosine (antioxidant) or Ca²⁺ (intracellular messenger) on the NO/O₂^•- ratio was also investigated. Graphical Abstract Simultaneous detection of nitric oxide and superoxide in macrophage cell lysates.

Localization of Nitric Oxide in Wheat Roots by DAF Fluorescence

Nitric oxide is a free radical signal molecule. Various methods are available for measurement of NO. Out of all methods, fluorescent probes to localize NO is very widely used method. Diaminofluorescein in diacetate form (DAF-2DA) is most widely probe for NO measurement. This method is based on application of 4,5-diaminofluorescein diacetate (DAF-2DA) which is actively diffused into cells, once taken up by cells cytoplasmic esterases cleave the acetate groups to generate 4,5-diaminofluorescein; DAF-2. The generated DAF-2 can readily react with N2O3, which is an oxidation product of NO to generate the highly fluorescent DAF-2T (triazolofluorescein). There are various advantages and disadvantages associated with this method, but to its advantage in diffusion closely to NO producing sites, it is widely used for localization studies. Here, we describe method to make sections of the roots and localization of NO in roots subjected to hypoxic stress.

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.

Working with nitric oxide and hydrogen sulfide in biological systems

Nitric oxide (NO) and hydrogen sulfide (H2S) are gasotransmitter molecules important in numerous physiological and pathological processes. Although these molecules were first known as environmental toxicants, it is now evident that that they are intricately involved in diverse cellular functions with impact on numerous physiological and pathogenic processes. NO and H2S share some common characteristics but also have unique chemical properties that suggest potential complementary interactions between the two in affecting cellular biochemistry and metabolism. Central among these is the interactions between NO, H2S, and thiols that constitute new ways to regulate protein function, signaling, and cellular responses. In this review, we discuss fundamental biochemical principals, molecular functions, measurement methods, and the pathophysiological relevance of NO and H2S.

An integrated microfluidic device for monitoring changes in nitric oxide production in single T-lymphocyte (Jurkat) cells

A considerable amount of attention has been focused on the analysis of single cells in an effort to better understand cell heterogeneity in cancer and neurodegenerative diseases. Although microfluidic devices have several advantages for single cell analysis, few papers have actually demonstrated the ability of these devices to monitor chemical changes in perturbed biological systems. In this paper, a new microfluidic channel manifold is described that integrates cell transport, lysis, injection, electrophoretic separation, and fluorescence detection into a single device, making it possible to analyze individual cells at a rate of 10 cells/min in an automated fashion. The system was employed to measure nitric oxide (NO) production in single T-lymphocytes (Jurkat cells) using a fluorescent marker, 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM DA). The cells were also labeled with 6-carboxyfluorescein diacetate (6-CFDA) as an internal standard. The NO production by control cells was compared to that of cells stimulated using lipopolysaccharide (LPS), which is known to cause the expression of inducible nitric oxide synthase (iNOS) in immune-type cells. Statistical analysis of the resulting electropherograms from a population of cells indicated a 2-fold increase in NO production in the induced cells. These results compare nicely to a recently published bulk cell analysis of NO.

A multilevel analytical approach for detection and visualization of intracellular NO production and nitrosation events using diaminofluoresceins

Diaminofluoresceins are widely used probes for detection and intracellular localization of NO formation in cultured/isolated cells and intact tissues. The fluorinated derivative 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM) has gained increasing popularity in recent years because of its improved NO sensitivity, pH stability, and resistance to photobleaching compared to the first-generation compound, DAF-2. Detection of NO production by either reagent relies on conversion of the parent compound into a fluorescent triazole, DAF-FM-T and DAF-2-T, respectively. Although this reaction is specific for NO and/or reactive nitrosating species, it is also affected by the presence of oxidants/antioxidants. Moreover, the reaction with other molecules can lead to the formation of fluorescent products other than the expected triazole. Thus additional controls and structural confirmation of the reaction products are essential. Using human red blood cells as an exemplary cellular system we here describe robust protocols for the analysis of intracellular DAF-FM-T formation using an array of fluorescence-based methods (laser-scanning fluorescence microscopy, flow cytometry, and fluorimetry) and analytical separation techniques (reversed-phase HPLC and LC-MS/MS). When used in combination, these assays afford unequivocal identification of the fluorescent signal as being derived from NO and are applicable to most other cellular systems without or with only minor modifications.

Microchip electrophoresis with amperometric detection for the study of the generation of nitric oxide by NONOate salts

Microchip electrophoresis (ME) with electrochemical detection was used to monitor nitric oxide (NO) production from diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA/NO) and 1-(hydroxyl-NNO-azoxy)-L-proline disodium salt (PROLI/NO). NO was generated through acid hydrolysis of these NONOate salts. The products of acid hydrolysis were introduced into a 5-cm separation channel using gated injection. The separation was accomplished using reverse polarity and a background electrolyte consisting of 10 mM boric acid and 2 mM tetradecyltrimethylammonium bromide, pH 11. Electrochemical detection was performed using an isolated potentiostat in an in-channel configuration. Potentials applied to the working electrode, typically higher than +1.0 V vs. Ag/AgCl, allowed the direct detection of nitrite, NO, DEA/NO, and PROLI/NO. Baseline resolution was achieved for the separation of PROLI/NO and NO while resolution between DEA/NO and NO was poor (1.0 ± 0.2). Nitrite was present in all samples tested.

Methods of nitric oxide detection in plants: a commentary

Over the last decade nitric oxide (NO) has been shown to influence a range of processes in plants. However, when, where and even if NO production occurs is controversial in several physiological scenarios in plants. This arises from a series of causes: (a) doubts have arisen over the specificity of widely used 4,5-diaminofluorescein diacetate (DAF-2DA)/4-amino-5-methylamino-2,7-difluorofluorescein (DAF-FM) dyes for NO, (b) no plant nitric oxide synthase (NOS) has been cloned, so that the validity of using mammalian NOS inhibitors to demonstrate that NO is being measured is debatable, (c) the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide (cPTIO) needs to be used with caution, and (d) some discrepancies between assays for in planta measurements and another based on sampling NO from the gas phase have been reported. This review will outline some commonly used methods to determine NO, attempt to reconcile differing results obtained by different laboratories and suggest appropriate approaches to unequivocally demonstrate the production of NO.

Biochemistry of mobile zinc and nitric oxide revealed by fluorescent sensors

Biological mobile zinc and nitric oxide (NO) are two prominent examples of inorganic compounds involved in numerous signaling pathways in living systems. In the past decade, a synergy of regulation, signaling, and translocation of these two species has emerged in several areas of human physiology, providing additional incentive for developing adequate detection systems for Zn(II) ions and NO in biological specimens. Fluorescent probes for both of these bioinorganic analytes provide excellent tools for their detection, with high spatial and temporal resolution. We review the most widely used fluorescent sensors for biological zinc and nitric oxide, together with promising new developments and unmet needs of contemporary Zn(II) and NO biological imaging. The interplay between zinc and nitric oxide in the nervous, cardiovascular, and immune systems is highlighted to illustrate the contributions of selective fluorescent probes to the study of these two important bioinorganic analytes.

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.

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.

Exogenous vs. endogenous gamma-glutamyltransferase activity: Implications for the specific determination of S-nitrosoglutathione in biological samples

The determination of S-nitrosoglutathione (GSNO) levels in biological fluids is controversial, partly due to the laborious sample handling and multiple pretreatment steps required by current techniques. GSNO decomposition can be effected by the enzyme gamma-glutamyltransferase (GGT), whose involvement in GSNO metabolism has been suggested. We have set up a novel analytical method for the selective determination and speciation of GSNO and its metabolite S-nitrosocysteinylglycine, based on liquid chromatography separation coupled to on-line enzymatic hydrolysis of GSNO by commercial GGT. In a post-column reaction coil, GGT allows the specific hydrolysis of the gamma-glutamyl moiety of GSNO, and the S-nitrosocysteinylglycine (GCNO) thus formed is decomposed by copper ions originating oxidized cysteinylglycine and nitric oxide (NO). NO immediately reacts with 4,5-diaminofluorescein (DAF-2) forming a triazole derivative, which is detected fluorimetrically. The limit of quantitation (LOQc) for GSNO and GCNO in plasma ultrafiltrate was 5 nM, with a precision (CV) of 1-6% within the 5-1500 nM dynamic linear range. The method was applied to evaluate the recovery of exogenous GSNO after addition of aliquots to human plasma samples presenting with different total GGT activities. By inhibiting GGT activity in a time dependent manner, it was thus observed that the recovery of GSNO is inversely correlated with plasmatic levels of endogenous GGT, which indicates the need for adequate inhibition of endogenous GGT activity for the reliable determination of endogenous GSNO.

Analytical chemistry of nitric oxide

Nitric oxide (NO) is the focus of intense research primarily because of its wide-ranging biological and physiological actions. To understand its origin, activity, and regulation, accurate and precise measurement techniques are needed. Unfortunately, analytical assays for monitoring NO are challenged by NO's unique chemical and physical properties, including its reactivity, rapid diffusion, and short half-life. Moreover, NO concentrations may span the picomolar-to-micromolar range in physiological milieus, requiring techniques with wide dynamic response ranges. Despite such challenges, many analytical techniques have emerged for the detection of NO. Herein, we review the most common spectroscopic and electrochemical methods, with a focus on the underlying mechanism of each technique and on approaches that have been coupled with modern analytical measurement tools to create novel NO sensors.

Use of diaminofluoresceins to detect and measure nitric oxide in low level generating human immune cells

Nitric oxide ((*)NO) has been implicated in multiple physiological and pathological immune processes. Different methods have been developed to detect and quantify (*)NO, where one of the principal difficulties are the accurately detection in cellular system with low levels of (*)NO production. The choice of the (*)NO detection method to be used depends on the characteristics of the experimental system and the levels of (*)NO production which depend on either the organism source of samples or the experimental conditions. Recently, high sensitive methods to detect and image (*)NO have been reported using 4,5-diaminofluorescein-based fluorescent probes (DAF) and its derivate 4,5-diaminofluorescein diacetate (DAF-2 DA). This work was aimed to adapt and optimize the use of DAF probes to detect and quantify the (*)NO production in systems of high, moderate and low out-put production, especially in human PBMC and their subpopulations. Here, we report an original experimental design which is useful to detect and estimate (*)NO fluxes in human PBMC and their subpopulations with high specificity and sensitivity.

Determination of ascorbic acid in individual rat hepatocyte cells based on capillary electrophoresis with electrochemiluminescence detection

A novel method to detect ascorbic acid (AA) in individual rat hepatocyte cells was developed by combining CE with electrochemiluminescence (ECL) based on tris(2,2'-bipyridine) ruthenium(II) (Ru(bpy)(3)2+). A single cell, followed by 0.1% SDS as cell lysis solution, was injected into the inlet of the separation capillary by electromigration. After optimizing the analytical conditions, the RSDs of migration time and peak height were 0.38% and 2.6% for 1.0x10(-5) M AA (n=10), respectively. The linear range of AA was from 1.0x10(-8) to 5.0x10(-5) M with a correlation coefficient of 0.9979 and the LOD (S/N=3) was estimated to be 1.0x10(-8) M. This method has been successfully applied to determine AA in single rat hepatocytes and the amount of AA in seven rat hepatocytes ranged from 16 to 62 fmol. The above results demonstrated that CE coupled with ECL is convenient, sensitive, and will become an attractive alternative method for single-cell analysis.

Chemical analysis of single cells

Chemical analysis of single cells requires methods for quickly and quantitatively detecting a diverse array of analytes from extremely small volumes (femtoliters to nanoliters) with very high sensitivity and selectivity. Microelectrophoretic separations, using both traditional capillary electrophoresis and emerging microfluidic methods, are well suited for handling the unique size of single cells and limited numbers of intracellular molecules. Numerous analytes, ranging from small molecules such as amino acids and neurotransmitters to large proteins and subcellular organelles, have been quantified in single cells using microelectrophoretic separation techniques. Microseparation techniques, coupled to varying detection schemes including absorbance and fluorescence detection, electrochemical detection, and mass spectrometry, have allowed researchers to examine a number of processes inside single cells. This review also touches on a promising direction in single cell cytometry: the development of microfluidics for integrated cellular manipulation, chemical processing, and separation of cellular contents.

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

Spatial measurements of nitric oxide (NO) production are important to understand the function and metabolism of this molecule. The reagent, 4,5-diaminofluorescein (DAF-2) and several structurally similar probes are widely used for detection and imaging of NO. However, DAF-2 also reacts with dehydroascorbic acid (DHA) in biological samples, with both products having nearly indistinguishable fluorescence spectra. Measurements using fluorimetry and fluorescence microscopy cannot easily differentiate NO-related fluorescent signals from DHA-related signals. While DAFs and the structurally related diaminorhodamines (DARs) both react with NO and DHA, they do so to different extents. We report a multiderivatization method to image NO and DHA simultaneously by using both DAF and DAR. Specifically, DAF-2 and DAR-4M are used to image NO and DHA concentrations; after reaction, the solutions are excited, at 495 nm to measure fluorescence emission from DAF-2, and at 560 nm to measure fluorescence emission from DAR-4M. Using the appropriate calibrations, images are created that depend either on the relative NO or the relative DHA concentration, even though each probe reacts to both compounds. The method has been validated by imaging NO production in both undifferentiated and differentiated pheochromocytoma (PC12) cells.

Repeatability of chemical cytometry: 2-DE analysis of single RAW 264.7 macrophage cells

This report presents the use of 2-DE with ultrasensitive fluorescence detection as a chemical cytometry tool to characterize the protein and biogenic amine content of single cells from the RAW 264.7 murine macrophage cell line. Cells were sorted by cell cycle prior to 2-DE analysis. Cells in the G2/M phase of the cell cycle were aspirated into the first-dimensional capillary and lysed. The cellular contents were fluorescently labeled and first separated by capillary sieving electrophoresis (CSE). Over 380 fractions were transferred from the first-dimensional capillary to the second-dimensional capillary, where components were further separated by MEKC and detected by laser-induced fluorescence. Twenty-five spots common to the four electropherograms were fit with a 2-D Gaussian surface to determine spot position, width, and amplitude. The RSD in CSE mobility was 1.0 +/- 0.6%. The mean uncertainty in spot position was 1.3 times larger than the mean spot width in the CSE dimension. The average SD in MEKC migration time was 0.37 +/- 0.13 s, which is smaller than the average spot size in this dimension. Spot capacity was 200. The RSD in spot amplitude was 50%, reflecting a large cell-to-cell variation in component expression.

Ubiquitous presence of argininosuccinate at millimolar levels in the central nervous system of Aplysia californica

Endogenous nitric oxide (NO) is generated by nitric oxide synthases (NOSs), which convert arginine (Arg) and oxygen to citrulline (Cit) and NO. Cit can be enzymatically transformed back to Arg by argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL) via a pathway involving argininosuccinate (ArgSuc). Arg, Cit, and ArgSuc levels have been measured in single neurons, neuronal clusters, and neuropil from the nervous system of the common neurobiological model Aplysia californica. Using capillary electrophoresis with laser-induced fluorescence detection, ArgSuc was found to be present in the nervous system in millimolar concentrations at levels significantly exceeding Cit levels (p<0.01). ArgSuc levels are proportional to Arg concentrations in single neurons, whereas they have no clear correlation to the Cit or Arg/Cit ratio. NOS-expressing neurons often exhibit fixative-resistant nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) staining. Incubation of ganglia with Arg results in an increase in Cit and ArgSuc levels in the NADPH-d-positive neuropil with no effect on ArgSuc levels in NADPH-d-negative neurons, suggesting NOS activity in the neuropil. Similar incubation with Cit leads to decreased ArgSuc levels in NADPH-d-negative neurons. These results can be explained by localization of NOS and ASS in different neurons; therefore, the complete Arg-Cit-NO cycle may not be present in the same neuron. The surprisingly high intracellular ArgSuc concentration suggests alternative sources of ArgSuc and that at least a portion may be formed by the reverse reaction of ASL (catalyzing the conversion of Arg to ArgSuc), which can be inhibited by Cit.

Recent advances in capillary electrophoretic analysis of individual cells

Because variability exists within populations of cells, single-cell analysis has become increasingly important for probing complex cellular environments. Capillary electrophoresis (CE) is an excellent technique for identifying and quantifying the contents of single cells owing to its small volume requirements and fast, efficient separations with highly sensitive detection. Recent progress in both whole-cell and subcellular sampling has allowed researchers to study cellular function in the areas of neuroscience, oncology, enzymology, immunology, and gene expression.