Neutral amino acids monitoring in phenylketonuric plasma microdialysates using micellar electrokinetic chromatography and laser-induced fluorescence detection

A ketogenic diet modifies glutamate, gamma-aminobutyric acid and agmatine levels in the hippocampus of rats: A microdialysis study

The ketogenic diet (KD) is acknowledged as an unconventional option in the treatment of epilepsy. Several lines of investigation point to a possible role of glutamate and gamma-aminobutyric acid (GABA) as main contributors in this protective effect. Other biomolecules could also be involved in the beneficial consequence of the KD, for example, the diamine agmatine has been suggested to block imidazole and glutamate NMDA receptor and serves as an endogenous anticonvulsant in different animal models of epilepsy. In the present report, we have used microdialysis coupled to capillary electrophoresis to monitor microdialysate levels of GABA, glutamate and agmatine in the hippocampus of rats submitted to a KD for 15days compared to rats on a normal rat chow diet. A significant increase in GABA and agmatine levels while no change in glutamate levels was observed. These results support the notion that the KD modifies different transmitters favoring inhibitory over excitatory neurotransmitters.

Amino acid profile of plasma and cerebrospinal fluid in preeclampsia

OBJECTIVES

To determine patterns in amino acids (arginine, GABA, glutamate and glutamine) and the diamine (agmatine) in plasma and cerebrospinal fluid (CSF) of mild and severe preeclampsia compared to control patients, using capillary zone electrophoresis to generate methods for refining diagnosis and prognosis and shed light on the pathophysiological mechanisms of preeclampsia.

STUDY DESIGN

This is an observational case-control study in pregnant women that attended the emergency ward of the University Hospital, Mérida, Venezuela, during the period April, 2009-April 2010.

MAIN OUTCOME MEASURES

Molar concentration of amino acids and diamine in plasma and CSF in control, mild and severe preeclampsia patients.

RESULTS

An increase in glutamate plasma levels was observed in mild preeclampsia and even higher in severe patients, while a biphasic response occurred in the CSF samples with a significant increment in mild preeclampsia patients and a decrease in severe preeclampsia patients. GABA significantly decreased both in plasma and CSF in mild preeclampsia with a tendency to return to normal levels in severe preeclampsia patients. Arginine CSF and plasma levels decreased in mild preeclampsia patients and even more in severe preeclampsia while agmatine significantly increased in plasma levels with no changes in CSF.

CONCLUSIONS

The results are discussed in terms of molecules that could be used as biomarkers of the severity of the disease and the possible involvement of these substances in the pathophysiology of preeclampsia.

Spectrofluorimetric determination of phenylalanine based on fluorescence enhancement of europium ion immobilized with sol-gel method

The analysis of phenylalanine (Phe) in serum is widely performed for the screening of newborn phenylketonuria (PKU). In this work, a novel spectrofluorimetric method for the determination of Phe was developed based on the fluorescence enhancement of Ruhemann's purple, the reaction product between Phe and ninhydrin, upon coordination with Eu(3+). A filter paper disc containing immobilized reactants (ninhydrin and Eu(3+)) was fabricated by sol-gel method. The experimental parameters affecting the determination of Phe, such as the concentrations of immobilized reagents, the pH value, the reaction time and temperature were optimized. Under optimum conditions, the fluorescence intensity of Phe-ninhydrin-Eu(3+) system was linearly proportional to the concentration of Phe in the range from 5×10(-5) to 2×10(-3) mol L(-1), and the limit of detection was found to be 5.2×10(-6) mol L(-1). The relative standard deviation was 2.6% for ten replicate measurements of 1.5×10(-4) mol L(-1) of Phe. The method has merits of sensitivity, simplicity and low cost, and has been applied to the determination of Phe in artificial serum.

Quantification of neurotransmitter amino acids by capillary electrophoresis laser-induced fluorescence detection in biological fluids

The role of neurotransmitter amino acids (NAAs) in the functioning of the nervous system has been the focus of increasingly intense research over the past several years. Among the various amino acids that have important roles as neurotransmitters, there are alanine (Ala), glutamic acid (Glu), aspartic acid (Asp), serine (Ser), taurine (Tau) and glycine (Gly). NAAs are present in plasma, cells and--at trace levels--in all biological fluids, but complex components in biological matrices make it difficult to determine them in biological samples. We describe a new capillary electrophoresis (CE) method with laser-induced fluorescence detection by which analytes are resolved in less than 12 minutes in a 18 mmol/L phosphate run buffer at pH 11.6. The use of elevated temperatures during sample derivatization leads to a drastic reduction in the reaction time, down to 20 min, compared to the 6-14 h usually described for reactions between FITC and amino acids at room temperature. In order to demonstrate its wide range of applications, the method was applied to the analysis of NAA in human plasma and in other sample types, such as red blood cells, urine, cultured cells, cerebrospinal fluid, saliva and vitreous humor, thus avoiding the typical limitations of other methods, which are normally suitable for use with only one or two matrix types.

Development of micellar electro kinetic chromatography for the separation and quantitation of L-valine, L-leucine, L-isoleucin and L-phenylalanine in human plasma and comparison with HPLC

Phenylketonuria (PKU) and Maple Syrup Urine Disease (MSUD) are two inborn metabolic diseases which are carried by autosomal recessive genes in man. These genetic errors result in accumulation of phenylalanine (in PKU) or valine, leucine and isoluecin (in MSUD). At high concentrations, amongst other problems, these amino acids cause mental retardation. However if detected early after birth, using special diets and other forms of therapy, mental abnormalities can be prevented. As a result in many countries screening of infants for MSUD and PKU, by measuring plasma amino acids has become a routine neonatal test. Capillary Electrophoresis (CE) assays have a number of advantages over the traditional chromatography techniques (such as GC or HPLC). These include low cost, high speed of analysis and high resolution. These characteristics, make CE an ideal method for the screening of inborn errors of metabolism. We developed a CE assay based on pre-column derivatisation of amino acids with phenylisothiocyanate. This conjugate has strong absorbance at 254 nm. CE was carried out using a Spectraphoresis 1000 instrument, fitted with 40 cm of a 25 microm capillary, at 17 degrees C. A running voltage of 18KV was used to separate the amino acid mixture in an electrophoretic buffer containing 45 mM imidazole, 6 mM borate and 208 mM SDS, fixed at pH 9 with 2-N-morpholino ethane sulfonic acid. The assay was calibrated using various concentrations of amino acid standards. LOD, LOQ, recovery, inter-day and intra-day variations of the assay were determined. Also, levels of the 4 amino acids in normal and abnormal plasma were determined and compared with HPLC.

Determination of amino acids in saliva using capillary electrophoresis with fluorimetric detection

In the present study a sensitive method for the quantification of main free amino acids in saliva using capillary electrophoresis with laser induced fluorescence detection was developed. As background electrolyte 20 mM borate buffer pH 9.5 was used. Amino acids were separated after derivatization with fluorescein isothiocyanate (FITC) and the conditions for derivatization were optimized. The main amino acids occurring in saliva (Pro, Ser, Gly and Glu) were separated in less than 7 min. The parameters of validation such as linearity of response, precision and detection limits were determined. The detection limits were obtained in the range from 0.1 to 2.4 nM. The developed method was employed for determination of amino acids in real saliva samples.

Development of microwave-assisted derivatization followed by gas chromatography/mass spectrometry for fast determination of amino acids in neonatal blood samples

Analysis of amino acids in blood samples is an important tool for the diagnosis of neonatal amino acid metabolism disorders. In the work, a novel, rapid and sensitive method was developed for the determination of amino acids in neonatal blood samples, which was based on microwave-assisted silylation followed by gas chromatography/mass spectrometry (GC/MS). The amino acids were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) under microwave irradiation. The controlled reaction was carried out employing BSTFA under conventional heating at 120 degrees C for 30 min. Experimental results show that microwave irradiation can accelerate the derivatization reaction of amino acids with BSFTA, and much shorten analysis time. The method validations (linear range, detection limit, precision and recovery) were studied. Finally, the method was tested by determination of amino acids in neonatal blood by the measurement of their trimethylsilyl derivatives by GC/MS in electron impact (EI) mode. Two biomarkers of L-phenylalanine and L-tyrosine in phenylketonuria (PKU)-positive blood and control blood were quantitatively analyzed by the proposed method. The results demonstrated that microwave-assisted silylation followed by GC/MS is a rapid, simple and sensitive method for amino acid analysis and is also a potential tool for fast screening of neonatal aminoacidurias.

Determination of aromatic and branched-chain amino acids in plasma by HPLC with electrogenerated Ru(bpy)3(3+) chemiluminescence detection

An HPLC method is described for the electrochemiluminescence (ECL) detection of amino acids, following cycloaddition reaction of their amino groups with divinyl sulfone (DVS), using electrogenerated tris(bipyridine)ruthenium(III). The derivatization reaction conditions were examined, with the optimum conditions found to be 40 mM DVS (pH 8.0) at 50 degrees C for 15 min. Detection limits for the 15 amino acids examined varied greatly (0.04-8.0 pmol) using a standard solution by flow injection analysis (FIA). These optimized conditions were used for HPLC determination of the amino acids in human plasma. A linear relationship was obtained up to 100 pmol on a column for aromatic and branched-chain amino acids. Recoveries of Tyr, Met, Val, Leu, Ile, Phe and Trp when added to human plasma (1 micromol/10 ml plasma, n=5) were 101.5+/-1.1, 99.0+/-1.2, 98.0+/-1.4, 101.1+/-1.6, 95.1+/-1.6, 99.2+/-1.5 and 97.7+/-1.3 % (mean+/-S.D.) respectively. The concentrations of the amino acids in the plasma are in good agreement with other published data.

Development of a capillary electrophoretic method for the analysis of amino acids containing tablets

Ketosteril is an enteral medicinal product indicated for prevention and therapy in chronic renal insufficiency in connection with a low protein diet. Tablets of Ketosteril contain five essential amino acids like: Lys, His, Thr, Trp, Tyr and another five amino acids in the form of their hydroxy and keto analogues as calcium salts, that are: alpha-ketoleucine, alpha-ketoisoleucine, alpha-ketovaline, alpha-ketophenylalanine and alpha-hydroxymethionine. The composition of Ketosteril tablets is routinely tested with three LC methods. Capillary electrophoretic method seems to be a good alternative for amino acids and their analogues determination in multicomponent pharmaceuticals because of short analysis time and the possibility to assay all components during a single run without any pretreatment. Electrophoresis was performed in 50 microm I.D. fused-silica capillaries with 65 cm distance to the detector. Capillaries were installed in Waters Quanta 4000 electrophoretic equipment with a positive power supply and on-line UV detection at 214 nm. Separations were done in a buffer containing 40 mM Tris and 160 mM boric acid titrated with NaOH to pH 10. The method developed allows the separation of all investigated analytes with an efficiency of n = 230,000 and 20 min analysis time. The method was applied for determination of all components of Ketosteril in commercial tablets.

Gas chromatography-mass spectrometry method for determination of phenylalanine and tyrosine in neonatal blood spots

In this paper we developed a simple, rapid and sensitive method for the quantitative analysis of phenylalanine (Phe) and tyrosine (Tyr) in dried blood spots of newborns by gas chromatography-mass spectrometry (GC-MS). Phe and Tyr in blood samples were reacted with N-methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide at 120 degrees C for 30 min and their corresponding single derivatives were obtained. Phe and Tyr were determined by measurement of their derivatives by GC-MS in the selected ion monitoring mode. Contents of Phe and Tyr in blood spots were calculated by external standard method. The ratio of Phe to Tyr was used for neonatal screening for phenylketonuria. The present method only took a few minutes to perform and required minimal sample preparation. In addition it provided low detection limits of 1.2 micromol l(-1) for Phe and 1.6 micromol l(-1)for Tyr.

Biomedical applications of capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis (CE) is a high-efficiency analytical technique that has had a great impact as a tool in biomedical research, clinical and forensic practice in the last ten years. Only in one of the applications, the DNA analysis, it has had an explosive exponential growth in the last few years. This impact is expressed in an enormous amount of CE articles and many reviews. The CE advantages with respect to other analytical techniques: the required very small sample volume, rapid analysis, great resolution power and low costs, have made this technique ideal for the analysis of a numerous endogenous and exogenous substances present in biological fluids. The different modes of CE have been coupled to different detection techniques such as UV-absorbance, electrochemical, mass spectrometry and laser-induced fluorescence detection (LIFD) to detect different nature and molecular size separated analytes. This review focuses mostly on the applications of CE-LIFD, to measure drugs and endogenous neuroactive substances such as amino acids and monoamines, especially in microdialysis samples from experimental animals and humans. CE-LIFD trends are discussed: automated faster analysis with capillary array systems, resolution power improvement, higher detection sensitivity, and CE systems miniaturization for extremely small sample volume, in order to make CE easier and affordable to the lab bench or the clinical bed.

Improved method for the measurement of large neutral amino acids in biological matrices

A high-performance liquid chromatographic method for measuring neutral amino acids in rat sera, brain tissues, and perfusates was developed by using o-phthalaldehyde sulfite as a pre-column derivatization reagent. With the present method, it was possible to separate the neutral amino acids within a single run in 25 min, while the acidic amino acids were eluted near or at the solvent front. The recovery was above 88.8% with a relative standard deviation (RSD) below 4.2%. The within- and between-day assay reproducibility for the determination of rat serum amino acids showed RSDs below 1.35 and 7.61%, respectively. In the present study, the neutral amino acids were assayed with high sensitivity, accuracy and good reproducibility in a relatively short time and on a small sample size.

Interaction of surfactants with homologous series of peptides studied by reversed-phase thin-layer chromatography

The relative strength of interaction between anionic (SDS) and nonionic surfactant (octaethoxylated oleyl alcohol, GEN) and homologous series of peptides was determined by reversed-phase thin-layer chromatography (RP-TLC) carried out on alumina layers impregnated with paraffin oil. The relative strength of interaction was calculated and was correlated with the physicochemical parameters of peptides. It was established that each peptide interacted with both surfactants and with their mixture (1:1, m/m). The relative strength of interaction depended on the number of amino acid units in the peptide, side chain bulk and electronic properties and hydrophobicity of the amino acids. The impact of individual parameters highly depended on the character of surfactant. The data prove that the retention order of peptides can be modified by adding different surfactants and surfactant mixtures to the mobile phase resulting in improved separation.