Analytical methodology for assays of serum tryptophan metabolites in control subjects and newly abstinent alcoholics: preliminary investigation by liquid chromatography with amperometric detection

Low interleukin-17A production in response to fungal pathogens in patients with chronic granulomatous disease

Patients with chronic granulomatous disease (CGD) cannot produce reactive oxygen species (ROS) due to a genetic defect in the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system. Dysregulation of the L-tryptophan metabolism in mice with defects in NADPH oxidase, resulting in overproduction of interleukin (IL)-17, has been proposed to link ROS defects with hyperinflammation and susceptibility to pulmonary aspergillosis. In this study, we assessed the L-tryptophan metabolism and cytokine profiles in response to fungal pathogens in CGD patients. Peripheral blood mononuclear cells (PBMCs) from CGD patients showed increased production of IL-6, tumor necrosis factor-α, and interferon-γ upon stimulation with Aspergillus or Candida species, while IL-17A production was strikingly low compared with healthy controls. Indoleamine 2,3-dioxygenase expression was similar in PBMCs and neutrophils from CGD patients compared with healthy controls. Conversion of L-tryptophan to L-kynurenine, as measured by high-performance liquid chromatography, did not differ between CGD patients and healthy controls. Moreover, adding L-kynurenine to the cell cultures did not suppress fungal-induced IL-17A production. Although PBMCs of CGD patients produced more proinflammatory cytokines after stimulation, IL-17A production was strikingly low in response to fungal pathogens when compared with healthy controls. In addition, cells from CGD patients did not display a defective L-tryptophan metabolism.

Rapid Isocratic Liquid Chromatographic Separation and Quantification of Tryptophan and Six kynurenine Metabolites in Biological Samples with Ultraviolet and Fluorimetric Detection

A simple, rapid isocratic liquid chromatographic procedure with ultraviolet and fluorimetric detection is described for the separation and quantification of L-tryptophan (Trp) and six of its kynurenine metabolites (kynurenine, 3-hydroxykynurenine, and 3-hydroxyanthranilic, kynurenic, xanthurenic and anthranilic acids). Using the Perkin Elmer LC 200 system, a reverse phase Synergi 4 μ fusion-RP80 A column (250 × 4.6 mm) (Phenomenex), and a mobile phase of 10 mM sodium dihydrogen phosphate: methanol (73:27, by vol) at pH 2.8 and a flow rate of 1.0-1.2 ml/min at 37 °C, a run took ∼13 min. The run took <7 min at 40 °C and a 1.4 ml/min flow rate. Limits of detection of all 7 analytes were 5-72 nM and their recoveries from human plasma and rat serum and liver varied between 62% and 111%. This simple method is suitable for high throughput work and can be further developed to include quinolinic acid and other Trp metabolites.

Candida albicans dampens host defense by downregulating IL-17 production

IL-17 is one of the key cytokines that stimulate host defense during a Candida infection. Several studies have demonstrated the capacity of Candida albicans to induce a Th17 response. Surprisingly, experiments employing live C. ablicans demonstrated a specific downregulation of host IL-17 secretion in human blood mononuclear cells (PBMCs). By avoiding the direct contact of live C. albicans and PBMCs, we demonstrate that this inhibition effect is mediated by a soluble factor released by live C. albicans. However, this effect is due neither to the releasing of C. albicans pathogen-associated molecular patterns nor to the alteration of different Th cell subtypes. Rather, we found that live C. albicans shifts tryptophan metabolism by inhibiting IDO expression away from kynurenines and toward 5-hydroxytryptophan metabolites. In addition, we show that these latter 5-hydroxytryptophan metabolites inhibit IL-17 production. In conclusion, live C. albicans inhibits host Th17 responses by modulatory effects on tryptophan metabolism.

Anti-Aspergillus human host defence relies on type 1 T helper (Th1), rather than type 17 T helper (Th17), cellular immunity

Both interferon-gamma-producing type 1 T helper (Th1)- and interleukin-17 (IL-17)-producing Th17 cells have been proposed to be involved in anti-fungal host defence. Although invasive aspergillosis is one of the most severe human fungal infections, little is known regarding the relative importance of the Th1 versus Th17 cellular immune pathways for the human anti-Aspergillus host defence. Using human peripheral blood mononuclear cells and a system consisting of monocyte-derived macrophages with lymphocytes, we found that Aspergillus fumigatus is a weak inducer of human IL-17 but induces a strong Th1 response. These data were validated by the very low IL-17 levels in bronchoalveolar lavage fluid and serum of patients with invasive aspergillosis. Surprisingly, live A. fumigatus reduced IL-17 production induced by mitogenic stimuli. This effect was mediated through the propensity of A. fumigatus to metabolize tryptophan and release kynurenine, which modulates the inflammatory response through inhibition of IL-17 production. In conclusion, A. fumigatus does not stimulate production of IL-17 and human host defence against aspergillosis may not rely on potent Th17 responses.

CSF neurochemicals during tryptophan depletion in individuals with remitted depression and healthy controls

The purpose of this study was to examine the differential effects of acute tryptophan (TRP) depletion vs. sham condition on plasma, cerebrospinal fluid (CSF) biochemical parameters, and mood in the following three subject groups: (1) nine antidepressant-free individuals with remitted depression, (2) eight paroxetine-treated individuals with recently remitted depression, and (3) seven healthy controls. Plasma TRP decreased during TRP depletion and increased during sham condition (p<.01). CSF TRP and 5-hydroxyindoleacetic acid were lower during TRP depletion than sham condition (p<.01 each). During TRP depletion, CSF TRP correlated significantly with the plasma sum of large neutral amino acids (SigmaLNAA) (R=-.52, p=.01), but did not significantly correlate with plasma TRP (R=.15, p=.52). The correlation between CSF TRP and ratio of TRP to SigmaLNAA was R=.41 and p=.06 during TRP depletion, and R=-.44 and p=.04 during sham condition. A negative correlation trend was observed between CSF-TRP levels and peak Hamilton Depression Rating Scale scores during TRP depletion in patients recovered from depression (R=-.45, p=.07), but not in healthy controls (R=-.01, p=.98). CSF neuropeptide Y was higher during TRP depletion than sham condition (t=1.75, p<.10). These results illustrate the importance of assessing plasma SigmaLNAA when using the TRP depletion paradigm. The use of a single CSF sampling technique although practical may result in data acquisition limitations.

Serotonin shapes risky decision making in monkeys

Some people love taking risks, while others avoid gambles at all costs. The neural mechanisms underlying individual variation in preference for risky or certain outcomes, however, remain poorly understood. Although behavioral pathologies associated with compulsive gambling, addiction and other psychiatric disorders implicate deficient serotonin signaling in pathological decision making, there is little experimental evidence demonstrating a link between serotonin and risky decision making, in part due to the lack of a good animal model. We used dietary rapid tryptophan depletion (RTD) to acutely lower brain serotonin in three macaques performing a simple gambling task for fluid rewards. To confirm the efficacy of RTD experiments, we measured total plasma tryptophan using high-performance liquid chromatography (HPLC) with electrochemical detection. Reducing brain serotonin synthesis decreased preference for the safe option in a gambling task. Moreover, lowering brain serotonin function significantly decreased the premium required for monkeys to switch their preference to the risky option, suggesting that diminished serotonin signaling enhances the relative subjective value of the risky option. These results implicate serotonin in risk-sensitive decision making and, further, suggest pharmacological therapies for treating pathological risk preferences in disorders such as problem gambling and addiction.

Flow-injection chemiluminescence determination of tryptophan through its peroxidation and epoxidation by peroxynitrous acid

A flow-injection chemiluminescence method for the determination of tryptophan was proposed, which was based on an intense chemiluminescence of tryptophan in hydrogen peroxide-nitrite-sulfuric acid medium. The chemiluminescence reaction was attributed to peroxidation and epoxidation of tryptophan by peroxynitrous acid, and subsequent decomposition of the formed dioxetane. The chemiluminescence intensity was linear with tryptophan in the range of 6.0 x 10(-7) to 3.0 x 10(-5)mol l(-1) and the limit of detection (S/N=3) was 1.8 x 10(-7)mol l(-1). The proposed method was applied to the analysis of tryptophan in pharmaceutical preparations and human serum.

Screening for defects in tryptophan metabolism

We introduced a two-step procedure for the detection of defects in metabolism of tryptophan: (1) HPTLC (described previously) is suitable when starting the investigation, (2) two HPLC methods with isocratic elution and spectrophotometric detection are used at the next step, when pathological findings are to be confirmed and the individual metabolites quantified. The first method enables the assessment of tryptophan, 5-hydroxyindolylacetic acid, indolylacetic acid, indolylacryloylglycine, indolylacrylic acid and its possible precursors, namely indolyllactic and indolylpropionic acids. The second procedure is intended for the monitoring of anthranilic, 3-hydroxyanthranilic, kynurenic and xanthurenic acids, kynurenine, 3-hydroxykynurenine and indoxyl-sulfate. The same pre-treated sample is used for all methods.

Maternal, umbilical, and amniotic fluid concentrations of tryptophan and kynurenine after labor or cesarean section

A major route of tryptophan metabolism is via the hepatic and cerebral synthesis of kynurenine, a substance subsequently used by astrocytes in the brain for the production of the neuroactive substances kynurenic acid and quinolinic acid. Both kynurenic and quinolinic acids have been implicated in modulating the activity of excitatory amino acid pathways in the brain, the former as a neuroprotectant because of its antagonist properties, and the latter as an excitotoxin because of its agonist actions, at NMDA receptors. We therefore determined the concentrations of tryptophan and kynurenine in maternal venous and umbilical cord blood, and in amniotic fluid, of infants after labor and vaginal delivery, and after delivery by cesarean section. Concentrations of tryptophan and kynurenine were significantly higher in umbilical vein plasma compared with maternal venous plasma. Tryptophan and kynurenine concentrations in umbilical vein plasma and amniotic fluid were significantly higher after labor, compared with samples obtained from infants of the same gestational age delivered by cesarean section. There was no umbilical vein-to-artery concentration difference for kynurenine in samples obtained after either labor or cesarean section, but there was a significant gradient for tryptophan in samples obtained after vaginal delivery, indicating increased transfer of this amino acid during labor. There was a significant correlation between umbilical vein tryptophan and kynurenine concentrations for both the labor and cesarean section groups, and plasma kynurenine concentrations were also significantly correlated with both umbilical vein cortisol concentrations and the duration of the second stage of labor in the vaginally delivered infants. These results suggest that the placental transfer of tryptophan and the fetal synthesis of kynurenine are increased during labor. These findings have implications for understanding the vulnerability of the infant brain to ischemic/hypoxic damage in the perinatal period. By analogy with the adult brain, the molar ratio of these substances is likely to determine the susceptibility of the brain to seizure and excitotoxic damage.

Whole blood serotonin content, tryptophan concentrations, and impulsivity in anorexia nervosa

BACKGROUND

We hypothesized that anorectics with or without bulimic features would differ on impulsivity and indices of central serotoninergic function (high impulsivity being correlated with reduced serotoninergic function).

METHODS

For all patients impulsivity rating scales and questionnaires detailing severity of eating disorder were assessed, and whole blood serotonin concentration (5-HT), free and total tryptophan (TT) concentrations, and large neutral amino acids (LNAA) were assayed.

RESULTS

Nineteen patients with anorexia nervosa were included, 10 presented associated bulimic features and nine did not. Twelve healthy matched controls were also included. Our hypothesis was not verified. However, tryptophan concentration and the ratio of tryptophan concentration to LNAA allow us to separate controls from anorectics, whereas 5-HT concentration does not. Two significant and positive correlations were found: between impulsivity and anxiety in the total anorectic population, and between anxiety and serotonin in the impulsive group.

CONCLUSIONS

All measured peripheral biologic indices except 5-HT concentration may be of interest in this pathology. Impulsivity and anxiety seem to be two personality components involved in anorexia nervosa. This study lead us to the necessity of redefining impulsivity in anorexia nervosa.

High-performance liquid chromatographic analysis with electrochemical detection of biogenic amines using microbore columns

High-performance liquid chromatography with electrochemical detection (HPLC-ED) is a popular method for measuring biogenic amines, owing to its simplicity, versatility, sensitivity, and specificity. Recent developments in microbore column HPLC-ED have been facilitated by miniaturization of solvent delivery, column packing, sample injection and micro-flow cell construction. The aim of this paper is to present an overview of recent developments in microbore column HPLC-ED, in terms of advantages and limitations. This paper covers the recent advancements and important factors of HPLC-ED analysis of biogenic amines using microbore columns. Particular emphasis is placed on applying this technique to microdialysis, for which great sensitivity is required. Its potential in future biomedical applications is also discussed.

Abnormal alpha-aminoadipic acid excretion in a newborn with a defect in platelet aggregation and antenatal cerebral haemorrhage

alpha-Aminoadipic acid (alpha AA) is an intermediate in lysine metabolism. We report a new case with alpha AA excess in urine and plasma, without alpha-ketoadipic acid, in a full-term male child born to unrelated parents; he presented at 24h of life with seizures that failed to respond to phenobarbital, clonazepam, and Vigabatrin and death occurred on the 38th day of life. Brain imaging suggested antenatal haemorrhage. Small quantities of alpha AA were also detected in the blood and urine of both parents and a healthy brother, all three of whom exhibited the same defect in platelet aggregation as the deceased child. Both parents had decreased levels of plasma neopterin, a finding that might be related to the immunodeficiency described in other cases.

Quantification of L-tryptophan and L-kynurenine by liquid chromatography/electron capture negative ion chemical ionization mass spectrometry

In a number of infectious and inflammatory diseases, stimulation of the immune system can lead to increased accumulation of tryptophan metabolites via induction of kynurenine pathway enzymes in extrahepatic tissues. We developed a liquid chromatographic/mass spectrometric (LC/MS) method suitable for tracing the disposition of 13C isotopomers of L-tryptophan and L-kynurenine in various cultured cell, tissue slice, and whole animal model systems used to investigate tryptophan flux through the kynurenine pathway. The method employs extractive derivatization of the analytes and their 2H internal standards with pentafluorobenzyl bromide in order to enhance the negative ion chemical ionization (NICI) mass spectrometric response. Normal-phase liquid chromatographic separation of derivatized analytes was optimized using a silica column with organic solvents, followed by particle beam transfer and NICI-MS. Standard curves were linear over the range 1-250 ng per sample. Particle beam and mass spectrometric operating parameters were optimized with direct flow injections of 1-(methylamino) anthraquinone, which is an ideal test compound for the evaluation of LC/NICI-MS. The developed method was used to quantify the conversion of (13C6)L-tryptophan to (13C6)L-kynurenine by human monocytes (THP-1) stimulated with interferon-gamma, lung and brain tissue slices obtained from gerbils immune-stimulated with pokeweed mitogen. The effect of whole body immune stimulation on the plasma levels of endogenous L-kynurenine in mice stimulated with interferon-gamma was also quantified.

Determination of peptide 520 in human plasma using post-column photolysis with electrochemical detection in liquid chromatography

A simple LC method for the determination of peptide 520 in human plasma was developed. Based on micellar chromatography, sodium octyl sulphate (SOS) was added into the mobile phase in order to separate the peptide from human plasma components. The procedure was fast and sensitive for the determination of the peptide in untreated human plasma. The electrochemical (EC) detection limit for peptide 520 in human plasma was 0.5 microgram ml-1. Linearity of the calibration plot for peptide 520 in human plasma was 0.999. This approach represents a direct injection technique for the potential detection and analysis of numerous peptides in biofluids, besides just plasma, with absolute quantification.

High-performance liquid chromatographic determination of 3-hydroxykynurenine with fluorimetric detection; comparison of preovulatory phase and postovulatory phase urinary excretion

A high-performance liquid chromatographic assay for 3-hydroxykynurenine in human urine is described. A fluorescent derivative of 3-hydroxykynurenine was prepared, based on the reaction of the compound with p-toluenesulphonyl chloride in a basic medium. The analytical method for the measurement of the fluorescent compound employed a Tosoh ODS 80 column eluted with 10 mM potassium dihydrogenphosphate (pH 4.5) and acetonitrile (3:2, v/v) and detection at an excitation wavelength of 375 nm (10 nm bandpass) and an emission wavelength of 455 nm (10 nm bandpass). The column temperature was maintained at 25 degrees C. The detection limit was 3 pmol (673 pg) at a signal-to-noise ratio of 5:1. The fluorescent derivative of 3-hydroxykynurenine was eluted at ca. 12.5 min. The technique was applied to the analysis of human urine. The total analysis time was ca. 15 min.

High performance liquid chromatography as a tool in the definition of abnormalities in monoamine and tryptophan metabolites in cerebrospinal fluid from patients with neurological disorders

In this study we report the levels of 3-methoxy-4-hydroxyphenylglycol, 3,4-dihydroxyphenylacetic acid, homovallinic acid, tryptophan, 5-hydroxyindole-3-acetic acid and serotonin in lumbar cerebrospinal fluid (CSF) from patients with multiple sclerosis, cerebrovascular disease and muscular tension headache the later, as healthy controls. The separation of these substances was performed on a reversed phase column by ion pair high performance liquid chromatography and detection was made by a glassy carbon electrode set at +900 mV vs Ag+/AgCl. The whole separation was achieved within 25 min. Concentrations of all substances (10-1000 pmole/L) were linearly proportional to areas obtained. The system is sensitive, stable and reproducible. The significance of CSF levels of these metabolites from patients groups compared with healthy controls are discussed.

Optimization of conditions for the simultaneous separation of ten tryptophan metabolites using reversed-phase high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic (RP-HPLC) method for the separation of tryptophan and ten metabolites of tryptophan pyrrolase pathway has been developed by sequential optimization of mobile phase, by adjusting the pH, the concentration of triethylamine and the gradient elution. The baseline resolution of the compounds, by this optimized procedure, is obtained with an analysis time, including the re-equilibration period, of less than 30 min. We believe this is the first RP-HPLC method that can separate tryptophan and ten of its metabolites in a single chromatographic run.

Determination of urinary tryptophan and its metabolites along the nicotinic acid pathway by high performance liquid chromatography with ultraviolet detection

A fast and sensitive method is given for analysing urinary tryptophan and six of its metabolites on the nicotinic acid pathway. Kynurenine, tryptophan, 3-hydroxykynurenine, anthranilic acid, 3-hydroxyanthranilic acid, kynurenic acid and xanthurenic acid were isocratically eluted and completely resolved with a mobile phase of acetonitrile + sodium acetate buffer, pH 4.76 (4:96, v/v). The flow rate was 0.8 mL/min at the beginning and was then linearly increased to 1.2 after 6 min; after 14 min the flow was augmented from 1.2 to 2 mL/min. The effluent was monitored with a variable UV detector set at 254 nm for the first five peaks and at 280 and 325 nm for the penultimate peak and final peak. Analytical recoveries of the compounds after deproteinization varied between 64% and 98%. The reported method should enable one to examine easily, extensively, quantitatively and routinely urinary tryptophan and the most important metabolites of the nicotinic acid pathway.

A modified HPLC technique for simultaneous measurement of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in cerebrospinal fluid, platelet and plasma

A sensitive, reliable and simplified HPLC assay for simultaneous measurement of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in human cerebrospinal fluid (CSF), platelets and plasma is described. Perchloric acid is used for one step precipitation of proteins and extraction of 5-HT and 5-HIAA. Precision of the assay has been increased by calibration of the instrument using serotonin-free plasma spiked with known amount of standards and N-w-methyl-5-hydroxytryptamine as internal standard. Integration of the peaks and calculations are achieved by a preprogrammed data module using ratio method. As little as 20 pg/ml of serotonin in the deproteinated sample can be detected using this procedure. In a group of surgical patients, plasma 5-HT concentration is (Mean +/- S D) 3.4 +/- 2.7 ng/ml and that of platelet 748.3 +/- 448.3 ng/10(9) platelets. In CSF, 5-HT is found to be 3.3 +/- 3.4 ng/ml and 5-HIAA is 15.1 +/- 7.3 ng/ml. A good correlation (r = 0.648, p less than .0001) is observed between 5-HT and 5-HIAA in CSF.

Separation of tryptophan metabolites by reversed-phase high-performance liquid chromatography with amperometric and fluorescence detection

An isocratic method for the separation of most of the tryptophan metabolites in the oxidative degradation pathway is described. The chromatographic analysis utilizes the combined selectivity and sensitivity of amperometric and fluorimetric detection. The effect of pH, ionic strength and operating potential on retention times and detector responses are evaluated. The use of dual electrochemical cells at two operating potentials together with a programmable fluorescence detector allows for improved selectivity for the detection of metabolites. The sensitivity achieved with this method allows for the detection of the metabolites in biological fluids at the picomole level. The method has been used to monitor serum samples obtained during a tryptophan load test.

Fluorimetric determination of kynurenine in human serum by high-performance liquid chromatography coupled with post-column photochemical reaction with hydrogen peroxide

A high-performance liquid chromatographic method involving post-column photochemical reaction and fluorimetric detection has been developed for the determination of kynurenine in serum. Kynurenine was separated on a column of Capcell Pak C18 (resistant to pH 10). The mobile phase consisted of 0.05 M Na2B4O7-0.1 M KH2PO4 buffer (pH 8.5)-ethanol (97:3, v/v) containing 60 mM hydrogen peroxide. The post-column reagent, containing 60% (v/v) ethanol, was mixed with the mobile phase, which was irradiated with ultraviolet light to induce fluorescence. The recovery of kynurenine was 95.9 +/- 5.0% (n = 6). The method allows the determination of as little as 2 pmol of kynurenine.

High-voltage electrophoretic separation of tryptophan metabolites of the kynurenine pathway

An analytical separation method for tryptophan and its seven metabolites of the kynurenine pathway by high-voltage paper electrophoresis is presented. Anthranilic acid, 3-hydroxyanthranilic acid, kynurenic acid, kynurenine, nicotinic acid, quinolinic acid, xanthurenic acid and unmetabolized tryptophan are measured in urine. Using radioactive labelling and scintillation counting as a quantification method, the relative standard deviation varied from 3.5% to 14.4%, corresponding to kynurenine and nicotinic acid, respectively. The recovery of labelled tryptophan added to urine was 95%. An advantage of the electrophoretic method is the minor tailing of spots and, hence, a good resolution of the components. For the monovalent anions of the kynurenine pathway metabolites, a linear correlation (r = 0.9996) was found between the experimental relative electrophoretic mobility and the quantity M-2/3, where M is the molecular mass of the anion.

Rapid method for determining desmosine, isodesmosine, 5-hydroxylysine, tryptophan, lysinoalanine and the amino sugars in proteins and tissues

A rapid and sensitive chromatographic method is described for determining desmosine, isodesmosine, 5-hydroxylysine, tryptophan, lysinoalanine, glucosamine and galactosamine at picomole levels in protein and tissue hydrolysates. This method uses either an automated amino acid analyser with a 17.5 X 0.28 cm microcolumn packed with 6.0 +/- 0.5 micron spherical resin, thermostated at 52 degrees C, one buffer system (0.21 M sodium citrate, pH 5.125) and 3-nitrotyrosine as the internal standard, or conventional instruments using the same system but with larger diameter columns and resins (11.0 +/- 1.0 micron). This method should be especially valuable for determining collagen and elastin in tissue hydrolysates from the amounts of 5-hydroxylysine, and desmosine or isodesmosine present, respectively, and for studying protein hydroxylation, glycosylation, cross-linking formation, and the turnover rates of collagen and elastin in normal and diseased tissues.