Quantification of γ-aminobutyric acid in the heads of houseflies (Musca domestica) and diamondback moths (Plutella xylostella (L.)), using capillary electrophoresis with laser-induced fluorescence detection

Separation and determination of 3-hydroxyaspartate by online concentration capillary electrophoresis/laser-induced fluorescence with microwave-assisted derivatization

A chiral analytical method was proposed based on capillary electrophoresis with laser-induced fluorescence detection coupled with microwave-assisted derivatization for the simultaneous baseline separation and sensitive detection of four stereoisomers of 3-hydroxyaspartate. The derivatization reaction of 3-hydroxyaspartate with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole was greatly accelerated by microwave irradiation. Under the optimized conditions, the derivatization yield was increased by 20% and the derivatization time was shortened by 20 min when compared with those from conventional water bath heating. In addition, the sensitivity was improved by online sample concentration methods. The detection limit of l-threo-3-hydroxyaspartate obtained by large-volume sample stacking with polarity switching was 5.3 nmol/L, which was around 1000-fold lower than that of the capillary electrophoresis/laser-induced fluorescence without stacking. The excellent analytical performance in terms of linearity and precision was also achieved. Furthermore, the developed method was successfully applied to the determination of 3-hydroxyaspartate in the spiked urine, and satisfactory recoveries were obtained ranging from 90.5 to 107.0%.

Spatiotemporally different expression of alternatively spliced GABA receptor subunit transcripts in the housefly Musca domestica

Insect γ-aminobutyric acid (GABA) receptors are important as major inhibitory neurotransmitter receptors and targets for insecticides. The housefly GABA receptor subunit gene MdRdl is alternatively spliced at exons 3 (a or b) and 6 (c or d) to yield the variants of ac, ad, bc, and bd combinations. In the present study, the expression of the MdRdl transcript in the body parts and in the developmental stages of the housefly Musca domestica was examined by quantitative polymerase chain reaction using specific primers that amplify the combinations of alternative exons. The results indicated that the transcripts of MdRdl, including four combinations, were highly expressed in the adult stage. MdRdl_bd was the most abundant in the adult head. The expression pattern did not change in the adult stage over 7 days after eclosion. The expression level of the MdRdl _bd transcript in the female head was similar to that of the male head. In contrast, MdRdl _bc was the predominant transcript in the pupal head and the adult leg. Because the homomeric Rdl _bc GABA receptor has a high affinity for GABA, our results provide grounds for designing agonist or competitive-antagonist insecticides that target the orthosteric site of the GABA receptor containing this Rdl variant.

HPLC determination of γ-aminobutyric acid and its analogs in human serum using precolumn fluorescence labeling with 4-(carbazole-9-yl)-benzyl chloroformate

In this study, a simple analytical method for the determination of γ-aminobutyric acid, gabapentin, and baclofen by using high-performance liquid chromatography with fluorescence detection was developed. An amidogen-reactive fluorescence labeling reagent, 4-(carbazole-9-yl)-benzyl chloroformate was first used to sensitively label these analytes. The completed labeling of these analytes can be finished rapidly only within 5 min at the room temperature (25°C) to form 4-(carbazole-9-yl)-benzyl chloroformate labeled fluorescence derivatives. These labeled derivatives expressed strong fluorescence property with the maximum excitation and emission wavelengths of 280 and 380 nm, respectively. The labeled derivatives were analyzed using a reversed-phase Eclipse SB-C18 column within 10 min with satisfactory shapes. Excellent linearity (R²  > 0.995) for all analytes was achieved with the limits of detection and the limits of quantitation in the range of 0.25-0.35 and 0.70-1.10 μg/L, respectively. The proposed method was used for the simultaneous determination of γ-aminobutyric acid and its analogs in human serum with satisfactory recoveries in the range of 94.5-97.5%.

An update of the classical and novel methods used for measuring fast neurotransmitters during normal and brain altered function

To understand better the cerebral functions, several methods have been developed to study the brain activity, they could be related with morphological, electrophysiological, molecular and neurochemical techniques. Monitoring neurotransmitter concentration is a key role to know better how the brain works during normal or pathological conditions, as well as for studying the changes in neurotransmitter concentration with the use of several drugs that could affect or reestablish the normal brain activity. Immediate response of the brain to environmental conditions is related with the release of the fast acting neurotransmission by glutamate (Glu), γ-aminobutyric acid (GABA) and acetylcholine (ACh) through the opening of ligand-operated ion channels. Neurotransmitter release is mainly determined by the classical microdialysis technique, this is generally coupled to high performance liquid chromatography (HPLC). Detection of neurotransmitters can be done by fluorescence, optical density, electrochemistry or other detection systems more sophisticated. Although the microdialysis method is the golden technique to monitor the brain neurotransmitters, it has a poor temporal resolution. Recently, with the use of biosensor the drawback of temporal resolution has been improved considerably, however other inconveniences have merged, such as stability, reproducibility and the lack of reliable biosensors mainly for GABA. The aim of this review is to show the important advances in the different ways to measure neurotransmitter concentrations; both with the use of classic techniques as well as with the novel methods and alternant approaches to improve the temporal resolution.

Advance of CE and CEC in phytochemical analysis (2012–2013)

This article presents an overview of the advance of CE and CEC in phytochemical analysis, based on the literature not mentioned in our previous review papers [Chen, X. J., Zhao, J., Wang, Y. T., Huang, L. Q., Li, S. P., Electrophoresis 2012, 33, 168–179], mainly covering the years 2012–2013. In this article, attention is paid to online preconcentration, rapid separation, and sensitive detection. Selected examples illustrate the applicability of CE and CEC in biomedical, pharmaceutical, environmental, and food analysis. Finally, some general conclusions and future perspectives are given.

Analysis of cerebrospinal fluid γ-aminobutyric acid by capillary electrophoresis with laser-induced fluorescence detection

The measurement of γ-aminobutyric acid (GABA) is suitable for investigating various neurological disorders. In this study, a sensitive and selective method for free GABA quantification in cerebrospinal fluid (CSF) has been standardised. This method is based on CE with LIF detection using 4-fluoro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-F) as a derivatisating agent. The reaction conditions (NBD-F concentration, pH, temperature and reaction time) and the electrophoretic parameters (run buffer composition and pH and separation voltage) were optimised to obtain the maximum derivatisation efficiency and electrophoretic resolution. The best resolution was obtained using 200 mM sodium borate, 10 mM SDS, 8.5 mM β-CD, pH 10 and 20 kV voltage. The method was linear in the concentration range of 2.5-1000 nM with good inter- and intra-assay precision values. The effects of CSF handling on free GABA concentrations were also evaluated. Our results show that the time delay between CSF collection and freezing strongly increases the CSF GABA values. Age-related reference values were established in 55 paediatric controls. The influence of antiepileptic therapy on free CSF GABA was studied in 38 neuropaediatric patients. Significantly, higher GABA values were obtained in patients taking valproic acid or vigabatrin therapy, which are antiepileptic drugs that modulate GABA metabolism.

Simultaneous determination of polyamines and acetylpolyamines in human urine by capillary electrophoresis with fluorescence detection

There has been evidence linking elevated polyamines (PAs) and acetylpolamines (AcPAs) level and cancer. So the simultaneous analysis of these compounds has become important task for cancer diagnosis and antitumor drug monitoring. A simple, fast and inexpensive CZE-LIF method has been developed for the determination of cadaverine (CAD), putrescine (PUT), spermine (SPM), spermidine (SPD), acetylspermine (ASPM), and acetylspermidine (ASPD) in human urine using 4-chloro-7-nitro-2,1,3-benzooxadiazole as a fluorescent reagent. Labeling reaction conditions were systematically investigated and were found to be 20 mM borate buffer at pH 7.4, labeling reaction time, and temperature were 10 min and 70°C, respectively. Under these optimized conditions the four PAs, two AcPAs and the internal standard were separated in 6 min. An Exactive-MS with an ESI source was used for identification of the bis-derivative of the ASPM. The method was validated in term of linearity, LODs, repeatability, intra- and interday assays, recovery, and selectivity. The LODs for CAD, PUT, SPM, SPD, ASPM, and ASPD were found to be 7.6, 10.0, 9.0, 8.8,7.8, and 3.3 nM, respectively. The method was successfully applied for the analysis of PAs and AcPAs in healthy human urine samples.

Determination of neurotransmitter amino acids in mouse central nervous system by CE-LIF

An MEKC method with LIF detection has been developed for the determination of seven neurotransmitter amino acids (NAAs) using 1,3,5,7-tetramethyl-8-(N-hydroxysuccinimidyl butyric ester)difluoroboradiaza-S-indacene as the labeling reagent. After derivatization at room temperature for 30 min, the seven target NAAs including glycine, alanine, γ-aminobutyric acid, taurine, glutamine, glutamic acid, and aspartic acid were separated in running buffer, which consisted of 70 mM pH 4.00 H3 PO4 /Na3 PO4 buffer, 5.5 mM cetyltrimethyl ammonium bromide and 20% v/v acetonitrile within 17 min. The LODs were 2 ~ 14 × 10(-10) M without interference from other coexisting amino acids. The proposed method has been applied to the analysis of NAAs in the central nervous systems of healthy mice and those with Alzheimer's disease with recoveries of 92-104%.