Serum amino acid analysis with pre-column derivatization: comparison of the o-phthaldialdehyde and N,N-diethyl-2,4-dinitro-5-fluoroaniline methods

Substantially elevated serum glutamate and CSF GOT-1 levels associated with cerebral ischemia and poor neurological outcomes in subarachnoid hemorrhage patients

Brain injury and cerebral vasospasm during the 14 days after the subarachnoid hemorrhage (SAH) are considered the leading causes of poor outcomes. The primary injury induces a cascade of events, including increased intracranial pressure, cerebral vasospasm and ischemia, glutamate excitotoxicity, and neuronal cell death. The objective of this study was to monitor the time course of glutamate, and associated enzymes, such as glutamate-oxaloacetate transaminase (GOT1), glutamate-pyruvate transaminase (GPT) in cerebrospinal fluid (CSF) and serum, shortly after SAH, and to assess their prognostic value. A total of 74 participants participated in this study: 45 participants with SAH and 29 controls. Serum and CSF were sampled up to 14 days after SAH. SAH participants' clinical and neurological status were assessed at hospitalization, at discharge from the hospital, and 3 months after SAH. Furthermore, a logistic regression analysis was carried out to evaluate the ability of GOT1 and glutamate levels to predict neurological outcomes. Our results demonstrated consistently elevated serum and CSF glutamate levels after SAH. Furthermore, serum glutamate level was significantly higher in patients with cerebral ischemia and poor neurological outcome. CSF GOT1 was significantly higher in patients with uncontrolled intracranial hypertension and cerebral ischemia post-SAH, and independently predicted poor neurological outcomes.

Analysis of amino acid composition in proteins of animal tissues and foods as pre-column o-phthaldialdehyde derivatives by HPLC with fluorescence detection

Studies of protein nutrition and biochemistry require reliable methods for analysis of amino acid (AA) composition in polypeptides of animal tissues and foods. Proteins are hydrolyzed by 6M HCl (110°C for 24h), 4.2M NaOH (105°C for 20 h), or proteases. Analytical techniques that require high-performance liquid chromatography (HPLC) include pre-column derivatization with 4-chloro-7-nitrobenzofurazan, 9-fluorenyl methylchloroformate, phenylisothiocyanate, naphthalene-2,3-dicarboxaldehyde, 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate, and o-phthaldialdehyde (OPA). OPA reacts with primary AA (except cysteine or cystine) in the presence of 2-mercaptoethanol or 3-mercaptopropionic acid to form a highly fluorescent adduct. OPA also reacts with 4-amino-1-butanol and 4-aminobutane-1,3-diol produced from oxidation of proline and 4-hydroxyproline, respectively, in the presence of chloramine-T plus sodium borohydride at 60°C, or with S-carboxymethyl-cysteine formed from cysteine and iodoacetic acid at 25°C. Fluorescence of OPA derivatives is monitored at excitation and emission wavelengths of 340 and 455 nm, respectively. Detection limits are 50 fmol for AA. This technique offers the following advantages: simple procedures for preparation of samples, reagents, and mobile-phase solutions; rapid pre-column formation of OPA-AA derivatives and their efficient separation at room temperature (e.g., 20-25°C); high sensitivity of detection; easy automation on the HPLC apparatus; few interfering side reactions; a stable chromatography baseline for accurate integration of peak areas; and rapid regeneration of guard and analytical columns. Thus, the OPA method provides a useful tool to determine AA composition in proteins of animal tissues (e.g., skeletal muscle, liver, intestine, placenta, brain, and body homogenates) and foods (e.g., milk, corn grain, meat, and soybean meal).

Bioanalytical LC separation techniques for quantitative analysis of free amino acids in human plasma

The quantitative analysis of free amino acids in human plasma has become an important and essential analysis parameter in different areas of life sciences. Free amino acid concentrations in human plasma samples are generally determined by means of GC or LC after chemical derivatization followed by UV, fluorescent or MS detection of the amino acid derivatives. Derivatization of free amino acids is done either pre- or post-column, and the amino acid derivatives obtained posess improved chromatographic behavior, increased detection sensitivity and selectivity compared with non-derivatized free amino acids. This work gives an overview of different chemical derivatization methods applied and their liquid separation techniques in bioanalytical assays for quantitative free amino acid analysis in human plasma samples. Important plasma preparation procedures, pre- and post-column derivatization, and different LC separation techniques are presented.

Effect of feed rate on growth rate and antibody production in the fed-batch culture of murine hybridoma cells

Batch and fed-batch cultures of a murine hybridomacell line (AFP-27) were performed in a stirred tankreactor to estimate the effect of feed rate on growthrate, macromolecular metabolism and antibodyproduction. Macromolecular composition was foundto change dynamically during batch culture ofhybridoma cells possibly due to active production ofDNA, RNA and protein during the exponential phase.Antibody synthesis is expected to compete with theproduction of cellular proteins from the amino acidpool. Therefore, it is necessary to examine therelationship between cell growth in terms of cellularmacromolecules and antibody production. In this study,we searched for an optimum feeding strategy bychanging the target specific growth rate in fed-batchculture to give higher antibody productivity whileexamining the macromolecular composition. Concentratedglucose (60 mM) and glutamine (20 mM) in DR medium(1:1 mixture of DMEM and RPMI) with additional aminoacids were fed continuously to the culture and thefeed rate was updated after every sampling to ensureexponential feeding (or approximately constantspecific growth rate). Specific antibody productionrate was found to be significantly increased in thefed-batch cultures at the near-zero specific growthrate in which the productions of cellular DNA, RNA,protein and polysaccharide were strictly limited byslow feeding of glucose, glutamine and other nutrients. Possible implications of these results are discussed.

Sensitive and rapid method for amino acid quantitation in malaria biological samples using AccQ.Tag ultra performance liquid chromatography-electrospray ionization-MS/MS with multiple reaction monitoring

An AccQ*Tag ultra performance liquid chromatography-electrospray ionization-tandem mass spectrometry (AccQ*Tag-UPLC-ESI-MS/MS) method for fast, reproducible, and sensitive amino acid quantitation in biological samples, particularly, the malaria parasite Plasmodium falciparum is presented. The Waters Acquity TQD UPLC/MS system equipped with a photodiode array (PDA) detector was used for amino acid separation and detection. The method was developed and validated using amino acid standard mixtures containing acidic, neutral, and basic amino acids. For MS analysis, the optimum cone voltage implemented, based on direct infusion analysis of a few selected AccQ*Tag amino acids with multiple reaction monitoring, varied from 29 to 39 V, whereas the collision energy varied from 15 to 35 V. Calibration curves were built using both internal and external standardization. Typically, a linear response for all amino acids was observed at concentration ranges of 3 x 10(-3)-25 pmol/muL. For some amino acids, concentration limits of detection were as low as 1.65 fmol. The coefficients of variation for retention times were within the range of 0.08-1.08%. The coefficients of variation for amino acid quantitation, determined from triplicate UPLC-MS/MS runs, were below 8% on the average. The developed AccQ*Tag-UPLC-ESI-MS/MS method revealed good technical and biological reproducibility when applied to P. falciparum and human red blood cells samples. This study should provide a valuable insight into the performance of UPLC-ESI-MS/MS for amino acid quantitation using AccQ*Tag derivatization.

Effects of rapid or slow body mass reduction on body composition in adult rats

Whether the speed of body mass (BM) reduction influences the body composition is uncertain. To investigate the effects of rapid vs slow body mass reduction on body composition, rats were divided into three groups; fed ad libitum for 16-day (Control, C); received restricted food intake during 16-day to decrease BM slowly (Slow, S); or fed ad libitum for 13-days and fasted for the last 3 days to rapidly reach a BM comparable to that of S (Rapid, R). Drinking water was restricted for R on day 16 to rapidly decrease their BM. All rats trained during the study. Final BM and adipose tissues mass were similar for R and S, and both were lesser than C. The skeletal muscle mass did not decrease in R and S. The liver mass was lower in R and S than C, and the decrease tended to be greater in R than S. Both the stomach and small intestine masses were significantly lower in R than C, but did not differ between S and C. In conclusion, differences of the speed of BM reduction affect the splanchnic tissues, and the decrease in splanchnic tissue mass was greater with rapid than slow BM reduction.

Chromatofocusing of peptides and proteins using linear pH gradients formed on strong ion-exchange adsorbents

Although it is commonly believed that a column packing used for chromatofocusing must have an "even" buffering capacity in order to produce a linear pH gradient, it is demonstrated here that linear pH gradients suitable for chromatofocusing can be produced on a column packing having a minimal buffering capacity. In particular, if either a strong-acid cation-exchange column packing or a strong-base anion-exchange column packing is presaturated with either a weak acid titrated with a strong base, or a weak base titrated with a strong acid, respectively, to the initial pH, then a linear or nearly linear pH gradient can be formed using a polyampholyte elution buffer by taking advantage of the presence of small quantities of weak-acid or weak-base functional groups that generally exist on these types of column packings. Experimental and theoretical studies are used to demonstrate that such systems have potential advantages over traditional chromatofocusing methods in terms of the speed of the separation, the resolution achieved, and the range of applications possible. Among other techniques described, a method for separating tryptic peptides using chromatofocusing and a strong-acid cation-exchange column packing is demonstrated to be a useful alternative to capillary isoelectric focusing and ion-exchange chromatography using a salt gradient for this purpose.

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.

Analysis of amino acids in human serum by isocratic reversed-phase high-performance liquid chromatography with electrochemical detection

A simple, sensitive and reproducible isocratic high-performance liquid chromatography (HPLC) method has been developed for the determination of amino acids in human serum. The method involves precipitation of the serum proteins with methanol followed by pre-column derivatization of amino acids with o-phthalaldehyde-2-mercaptoethanol or o-phthalaldehyde-sodium sulfite. HPLC separation of the derivatives was performed using an ODS column with an isocratic mobile phase system and electrochemical detection (+0.75 V). The response was linear over the range 5-300 microM for all amino acids. The method allows quantitative determination of glutamic acid, asparagine, serine, glutamine, histidine, taurine, alanine, arginine, methionine, isoleucine, ornithine, leucine, phenylalanine, lysine and tryptophan at concentrations as low as 0.5-5.0 pmol (signal-to-noise ratio=2). Using this method, the levels of amino acids in serum from healthy donors and patients with ischemic stroke were determined.

State-of-the-art of high-performance liquid chromatographic analysis of amino acids in physiological samples

Nowadays, the fast and sensitive high-performance liquid chromatographic (HPLC) analysis of derivatized amino acids is a good alternative to the ion-exchange chromatography (IEC) method for plasma amino acids. However, several precautions have to be taken in order to obtain reliable data on the concentration of amino acids in physiological fluids. These include the collection, centrifugation, storage conditions and the method of deproteinization. Furthermore, the method of pre-column derivatization in connection with the protein precipitant used and the choice of the chromatographic system which determines the overall resolution are important factors. HPLC methods using pre-column derivatization with o-phthaldialdehyde were suitable for the accurate determination of many primary amino acids in plasma because of their high sensitivity, simplicity, speed and reliability. When the determination of secondary amino acids and cystine was also necessary, the phenylisothiocyanate method was the preferred technique. The intra-laboratory variability of the HPLC method was satisfactory while the inter-laboratory variation of this method was found to be similar to that of IEC, HPLC methods capable of separating over forty physiological amino acids seem promising for the analysis of urine samples.

Validation of the determination of amino acids in plasma by high-performance liquid chromatography using automated pre-column derivatization with o-phthaldialdehyde

A sensitive and reproducible fully automated method for the determination of amino acids in plasma based on reversed-phase high-performance liquid chromatography and o-phthaldialdehyde pre-column derivatization is described. A 5-microns Spherisorb ODS 2 column (125 x 3 mm I.D.) was selected for routine determination. Over 40 physiological amino acids could be determined within 49 min (injection to injection) and 48 samples could be processed unattended. The coefficients of variation for most amino acids in plasma were below 4%. We were also able to measure trace amounts of amino acids in plasma normally not detected in a routine analysis. The results obtained with the method described compared favourably with those of conventional amino acid analysis (r = 0.997) and were in excellent agreement with those of other laboratories (r = 0.999).

Effects of an acute increase in plasma triglyceride levels on glucose metabolism in man

The aim of the study was to evaluate the effects of an acute increase in triglyceride levels induced by Intralipid (Kabivitrum, Stockholm, Sweden) infusion on forearm glucose uptake, glucose oxidative metabolism, and hepatic glucose production independent of circulating free fatty acid (FFA) levels in man. Six normal subjects underwent three different tests in random order. Each test consisted of a control period of 120 minutes followed by a euglycemic, hyperinsulinemic clamp lasting 120 minutes. In test 1, a high-dose intravenous Intralipid infusion was performed to increase triglyceride and FFA levels. In test 2, heparin (30 U/min) plus low-dose Intralipid infusions were performed to maintain triglyceride at normal levels and increase only FFA levels. Test 3 was performed as a control study. During the 120-minute control period, forearm glucose uptake and hepatic glucose production were not affected by increasing only FFA levels (test 2) or FFA and triglyceride levels (test 1) as compared with the control study. On the contrary, glucose oxidation was significantly decreased as compared with the control study during tests 1 and 2, without a further significant decrease during simultaneously increased FFA and triglyceride levels. Concomitantly, lipid oxidation was similar in tests 1 and 2, at values significantly greater than in test 3. During the euglycemic clamp, forearm glucose uptake and glucose oxidation were significantly lower during tests 1 and 2 than test 3. At variance with the control period, the increase of triglyceride levels during test 1 caused a significant 30% to 40% decrease of both parameters as compared with test 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of amino acids in human plasma by liquid chromatography with postcolumn ninhydrin derivatization using a hydroxyapatite cartridge for precolumn deproteination

Amino acids in human plasma were determined by liquid chromatography with postcolumn ninhydrin derivatization using a hydroxyapatite cartridge for precolumn deproteination. S-Carboxymethyl-L-cysteine, D-phenylglycine and S-aminoethyl-L-cysteine were found to be suitable internal standards. The proposed method is simple, rapid (deproteination time less than 1 min) and reproducible [relative standard deviation below 3% except for low-level aspartic acid (n = 3)]. The average recovery of 25 amino acids was above 90%. The elution time of amino acids in human plasma was approximately 2 h. Protein binding of tryptophan was also determined by the proposed method. The analytical data for amino acids in human plasma deproteinated using the proposed and published methods (5-sulphosalicylic acid and ethanol) were compared.

Hypocaloric high-protein diet improves glucose oxidation and spares lean body mass: comparison to hypocaloric high-carbohydrate diet

The aim of the study was to investigate the effects of two hypocaloric (800-kcal) diets on body weight reduction and composition, insulin sensitivity, and proteolysis in 25 normal glucose-tolerant obese women. The two diets had the following composition: 45% protein, 35% carbohydrate (CHO), and 20% fat (HP diet, 10 subjects), and 60% CHO, 20% protein, and 20% fat (HC diet, 15 subjects); both lasted 21 days. A euglycemic hyperinsulinemic (25 mU/kg/h) clamp lasting 150 minutes combined with indirect calorimetry was performed before and after the diet. Both diets induced a similar decrease in body weight and fat mass (FM), whereas fat-free mass (FFM) decreased only after the HC diet. 3-Methylhistidine (3-CH3-HIS) excretion was reduced by 48% after the HP diet and remained unchanged after the HC diet (P < .05). A significant correlation was found between the changes in FFM and in 3-CH3-HIS excretion after the diet (rs = .50, P < .02). Blood glucose remained unchanged, while insulin decreased in both diets. Free fatty acids (FFA) significantly increased only after the HC diet (P < .05). During the clamp period, glucose disposal and glucose oxidation significantly increased after the HP diet and significantly decreased after the HC diet. Opposite results were found when measuring lipid oxidation. In conclusion, our experience suggests that (1) a hypocaloric diet providing a high percentage of natural protein can improve insulin sensitivity; and (2) conversely, a hypocaloric high-polysaccharide-CHO diet decreases insulin sensitivity and is unable to spare muscle tissue.

Derivatization of posttranslationally modified amino acids

After a brief overview of posttranslational modifications of protein amino acids, the use of various derivatizing reagents for amino acid analysis is discussed. Derivatization and chromatographic separation of hydroxyproline, methylhistidine, and phosphorylated amino acids are discussed in detail to illustrate some of the strategies that can be applied to the analysis of posttranslationally modified amino acids.

Derivatization reactions for neurotransmitters and their automation

Many reagents suitable for the derivatization of neurotransmitters are selective for the amino function. Others, however, are selective for the carboxyl-, thiol- and hydroxyl function, and recently, reagents selective for more than one function have been produced. Interest persists in the established reagents, with their well understood behaviour which assists automation of analysis as much as new technology. Workers appear reluctant to tackle the optimization of many novel reagents. Chiral reagents may become important if d-amino acids are shown to be significant from a physiological point of view. Solid-phase reagents offer better regulated chemistry and combined derivatization/solid-phase extraction, which make them an exciting prospect.

Rapid determination of glutamine in biological samples by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of glutamine in biological samples is presented. Glutamine was derivatized with ortho-phthalaldehyde reagent containing 3-mercaptopropionic acid and separated by reversed phase chromatography on a C18 column containing 3-microns particles. No interference from other amino acids was observed. The assay was linear over a range from 1 to 2,000 mumol/l. Analytical recovery of plasma samples spiked with glutamine was 98.6 +/- 3.8%. Within- and between-batch imprecision were 1.5% and 2.2%, respectively. The derivatization step was fully automated. Total analysis time, including derivatization and chromatography, amounted to 6 min. The method can be used for the determination of glutamine in plasma, urine, cerebrospinal fluid and tissue homogenates.

High-performance liquid chromatographic method with fluorescence detection for the determination of total homocyst(e)ine in plasma

A high-performance liquid chromatographic method for the determination of total plasma homocyst(e)ine [H(e)] after reduction with sodium tetrahydroborate and precolumn derivatization with o-phthaldialdehyde is described. The analyses, carried out on a reversed-phase C18 column, were based on spectrofluorimetric detection. The sensitivity was 1 pmol per injection and the intra- and inter-assay relative standard deviations were 1.8% and 5%, respectively. The plasma H(e) concentration determined in 40 healthy volunteers (20-60 years old) was 12.4 +/- 2.9 microM (mean +/- S.D.), in good agreement with reference values.