Adsorption of tryptophan metabolites from physiological fluids on XAD-2 and determination by single ion monitoring

Small phenolic and indolic gut-dependent molecules in the primate central nervous system: levels vs. bioactivity

INTRODUCTION

A rapidly growing body of data documents associations between disease of the brain and small molecules generated by gut-microbiota (GMB). While such metabolites can affect brain function through a variety of mechanisms, the most direct action would be on the central nervous system (CNS) itself.

OBJECTIVE

Identify indolic and phenolic GMB-dependent small molecules that reach bioactive concentrations in primate CNS.

METHODS

We conducted a PubMed search for metabolomic studies of the primate CNS [brain tissue or cerebrospinal fluid (CSF)] and then selected for phenolic or indolic metabolites that (i) had been quantified, (ii) were GMB-dependent. For each chemical we then conducted a search for studies of bioactivity conducted in vitro in human cells of any kind or in CNS cells from the mouse or rat.

RESULTS

36 metabolites of interests were identified in primate CNS through targeted metabolomics. Quantification was available for 31/36 and in vitro bioactivity for 23/36. The reported CNS range for 8 metabolites 2-(3-hydroxyphenyl)acetic acid, 2-(4-hydroxyphenyl)acetic acid, 3-(3-hydroxyphenyl)propanoic acid, (E)-3-(3,4-dihydroxyphenyl)prop-2-enoic acid [caffeic acid], 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, 2-acetamido-3-(1H-indol-3-yl)propanoic acid [N-acetyltryptophan], 1H-indol-3-yl hydrogen sulfate [indoxyl-3-sulfate] overlapped with a bioactive concentration. However, the number and quality of relevant studies of CNS neurochemistry as well as of bioactivity were highly limited. Structural isomers, multiple metabolites and potential confounders were inadequately considered.

CONCLUSION

The potential direct bioactivity of GMB-derived indolic and phenolic molecules on primate CNS remains largely unknown. The field requires additional strategies to identify and prioritize screening of the most promising small molecules that enter the CNS.

Determination of serotonin and 5-hydroxyindoleacetic acid in urine by reversed-phase ion-pair partition chromatography with fluorimetric detection

The determination of serotonin and 5-hydroxyindoleacetic acid in urine is described. The compounds are separated by means of reversed-phase chromatography using tri-n-butylphosphate as the stationary phase and a mobile phase containing perchlorate as an ion-pairing agent. Detection is performed fluorimetrically. The compounds can be assayed directly, using two mobile phases with different pH values. Alternatively, both compounds can be determined with the same mobile phase after urine extraction on a small XAD-2 column for clean-up of serotonin. Two different approaches were evaluated for this XAD-2 extraction, viz.: (i) desorption of serotonin with a methanol-rich solvent after a washing step with an aqueous solvent; (ii) direct desorption of serotonin in the washing step using a solvent with a small percentage of methanol. Only the latter approach proved to be successful. The linearity of the method was investigated by standard additions to urine. The method was applied to the determination of both compounds in urine. The stability of the compounds in standard solutions and in urine was investigated under various storage conditions.

Simultaneous analysis of twelve biogenic amine metabolites in plasma, cerebrospinal fluid and urine by capillary column gas chromatography-high-resolution mass spectrometry with selected-ion monitoring

A procedure is described for the simultaneous determination of twelve acidic and alcoholic metabolites of trace and catecholic biogenic amines in plasma, cerebrospinal fluid and urine by capillary column gas chromatography--high-resolution mass spectrometry. Protein precipitation with sulphosalicylic acid, derivatization with two different reagent systems, final sample clean-up with a buffer wash and a program for automatically changing the reference mass of the mass spectrometer to suit each group of compounds as they are eluted from the column, are the main novel features of the procedure. A brief description of the synthesis of the deuterium-labelled internal standards is provided. The procedure is applied to biological samples and a comparison to reported values is given.

Determination of tryptamine in brain tissue by capillary gas chromatography mass spectrometry (selected ion monitoring)

The development of an analytical method for the determination of brain tryptamine using capillary gas chromatography mass spectrometry (selected ion monitoring) is presented. The method involves solvent extraction of brain homogenates and further derivatization (pentafluoropropionyl derivatives) of the dried extracts. Gas chromatographic analysis is performed using a bonded phase silica fused capillary column. Selected monitoring of m/z 289 and 292 (isotope dilution technique) allows the determination of tryptamine in adult rat brain (450 +/- 73 pg g-1) (means +/- SEM), n = 6.

Thin-layer chromatographic determination of indolic tryptophan metabolites in human urine using Sep-Pak C18 extraction

Tryptophan and some of its indole metabolites were separated by thin-layer chromatography, stained with the Van Urk--Salkowski reagent, and quantitated by scanning densitometry. The application of this technique for the detection of the indoles in urine samples, employing Sep-Pak C18 cartridges for extraction, was demonstrated. The proposed method is simple and accurate. The detection limits were 2 micrograms/ml 5-hydroxytryptophan, 1.75 micrograms/ml 5-hydroxyindolyl-3-acetic acid, 1.5 micrograms/ml tryptophan, 0.8 micrograms/ml indolyl-3-acetic acid, 0.9 micrograms/ml indolyl-3-butyric acid, 1.75 micrograms/ml serotonin, and 1.25 micrograms/ml tryptamine.

In vivo studies of the tryptophan-5-hydroxylase system. Quantitation of serotonin and tryptamine using gas chromatography-mass fragmentography

An in vivo determination of tryptophan-5-hydroxylase (E.C. 1.14.16.4) activity is described. Subjects were loaded with deuterated L-tryptophan-d5 (50 mg/kg body weight) and the deuterated serotonin-d4 in urine was analysed using mass fragmentography. Four control subjects were dosed orally and two of them also intravenously with 50 mg/kg of L-tryptophan-d5. One patient with atypical phenylketonuria (PKU) due to a tetrahydrobiopterin (BH4) deficiency was dosed without and during BH4 treatment. Without BH4, the patient showed only minor formation of deuterated serotonin. After BH4 administration (2.5 mg/kg body weight) the serotonin formation increased about four-fold but was not normalized. Serotonin in urine and blood was analysed as the pentafluoropropionyl (PFP) derivative using gas chromatography-mass fragmentography. Deuterated serotonin was used as internal standard. The analysis of tryptamine can be performed with the same procedure.

Urinary neurotransmitter metabolites in drug-free chronic schizophrenic patients measured by gas chromatography selected positive ion monitoring

The free urinary metabolites, homovanillic, indoleacetic and 5-hydroxyindoleacetic acid were measured in 24 h urines obtained from seven highly selected drug-free chronic schizophrenic patients and seven mentally normal control subjects on a low amine diet. Gas chromatography selected ion monitoring of silylated extracts was used to assay each metabolite using its own deuterated form as an internal standard. In the electron impact mode the positive ion fragments used to quantitate the amount of each metabolite in the urine were, respectively, m/z 209/211 for homovanillic acid, 319/321 for indoleacetic acid and 290/292 for 5-hydroxyindoleacetic acid. It was found essential that each compound be assayed using its own deuterated derivative as the internal standard. When expressed per mg creatinine, the homovanillic and 5-hydroxyindoleacetic acid levels of the chronic schizophrenic patients were in the normal range, but indoleacetic acid was slightly and statistically significantly higher, p = 0.01.

Simultaneous determination of endogenous norepinephrine and dopamine-beta-hydroxylase activity in biological materials by chemical ionization mass fragmentography

A new clean-up procedure is described for the quantitation of biogenic amines and their metabolites by gas chromatography-chemical ionization mass fragmentography. The procedure is carried out in an acidic, non-aqueous medium. The metabolites as well as the amines are extracted with greater than 92% recovery. Using a CPG-10 column, the procedure is most suitable for the purification of these amines and their metabolites from the extract. It has been applied to the simultaneous determination of endogenous norepinephrine and dopamine-beta-hydroxylase (DBH) activity in rat adrenal by use of [2H2]dopamine as a substrate and [2H6]norepinephrine as an internal standard. The quantitation limit of the DBH activity is 0.1 pmole/mg of rat adrenal per hour.

Isolation of drugs from blood and tissues with XAD-2 bags

Nylon bags containing 2-g portions of Amberlite XAD-2 resin were used for systematic analysis of drugs in biosamples. The procedure requires 10 or less grams of material, two XAD-2 bags, and enables rapid and economical isolation of most common drugs. The method was demonstrated on autopsy blood spiked withe 19 of the most common drugs, and was routinely used in cases of fatal and non-fatal poisoning. The eluates were clean and suitable for direct gas chromatographic and ultraviolet spectrophotometric analysis. The procedure used appeared more convenient than XAD-2 column extraction procedures. Classic solvent extraction methods were usually less efficient.

Direct gas chromatograph-mass spectrometer connection of glass capillary columns for the analysis of serotonin and metabolites by selective ion monitoring

A direct connection system that requires no modifications to either the gas chromatograph or the mass spectrometer is described for the coupling of glass capillary columns to a commercial mass spectrometer. Vacuum-tight connections can be readily achieved with standard 1/16-in. fittings and septum discs. The system can be operated with column outlet helium flow-rates of 1.5-2 ml/min at ion source pressures of 2-5 - 10(-5) mmHg. Although an injector splitter of our own design has been used, the initial test results obtained with a splitless injection method based on the use of a solids injection syringe together with a packed column injector assembly indicate the feasibility of developing a totally splitless and connection system that is simple to use. The system has been applied to the detection of the pentafluoropropionyl derivatives of serotonin, methoxytryptamine, methoxytryptophol and 5-hydroxytryptophol by selective ion monitoring techniques. Column performances under both sets of conditions (gas-liquid chromatography alone and combined with mass spectrometry) are compared and the evaluation of direct versus indirect coupling showed yields of the order of 50% through the molecular separator.

Profiling of human body fluids in healthy and diseased states using gas chromatography and mass spectrometry, with special reference to organic acids

This review summarizes recent advances in the application of gas chromatography and mass spectrometry to the study of human diseases. Emphasis is placed upon the organic acid profiles of the various body fluids. Methods for sample work-up prior to separation and mass spectrometric analysis are reviewed, and artifacts and pitfalls are discussed. Organic acid profiles, obtained with packed or capillary columns attached to mass spectrometers with or without computer systems, have led to the discovery of new normal metabolites, new metabolic disorders, and to new knowledge about a number of other diseases. Stable isotopes and gas chromatography--mass spectrometry are suitable for quantitative analysis of many compounds in the body fluids, and well suited for investigation of metabolic pathways.

Gas chromatographic separation of histamine and its metabolites

A new, rapid and simple gas-liquid chromatographic method is described for the simultaneous determination of histamine, 1-methylhistamine, 4-imidazoleacetic acid and 1-methyl-4-imidazoleacetic acid. These compounds are derivatized at 60 degrees in one fast 30-min reaction with bis(trimethylsilyl)acetamide-trimethylchlorosilane and are then separated on OV-17. No previous methylation of the acids is needed. A complete profile of the four metabolites can be obtained in 8 min with baseline resolution, and there are no tailing effects. The quantitative response curves are linear in the nanogram range, with detection limits of the order of 10 ng for the acids and 100 ng for the amines. The structures of these new trimethylsilyl derivatives have been verified by combined gas-liquid chromatography-mass spectrometry.

Profiles of prostaglandins A, B, E and F (series I and II) obtained by gas chromatography with multiple-ion detection

A new method is presented for the simultaneous one-step derivatization of prostaglandins A1, A2, B1, B2, E1, E2, F1alpha and F2alpha with N,O-bis(trimethylsilyl)trifluoroacetamide-piperidine. The procedure provides stable and reproducible trimethylsilyl derivatives that show good chromatographic properties on OV-17 and OV-225 columns, and precludes any significant degree of interconversion of the prostaglandins. The prostaglandins F, B and E are determined as the corresponding tetrakis(trimethylsilyl), bis(trimethylsilyl) and 9-enol-tetrakis(trimethylsilyl) derivatives, respectively. The enolization of prostaglandins E proceeds quantitatively only if piperidine is added to the acetamide. This mixture also produces the novel derivative 9-piperidyl-tris(trimethylsilyl)prostaglandin A. Evidence is also presented on the quantitative injection losses due to the type of syringe used (1micronl or 10 micronl). A modified extraction procedure has been applied to samples of human seminal fluid. The procedure, which involves the centrifugation of the samples, allows the recovery of all of the prostaglandins in one fraction, which is then derivatized and screened by combined gas-liquid chromatography-multiple-ion detection techniques in order to identify the individual compounds.

Simultaneous analysis of catecholamine acidic metabolites by single ion monitoring and manual control of the magnetic field

A method for multicomponent analysis by single ion monitoring is presented. This method involves monitoring of one ion per selected compound in a GC run. To focus sequentially on each ion, the magnetic field strength of the mass spectrometer is manually reset to the proper value during the intervals between eluting peaks. Stationary phase bleeding provides a suitable reference background for rapid location of selected ions. This technique has been applied to the simultaneous analysis of 3,4-dihydroxyphenylacetic acid (DOPAC), vanillylmandelic acid (VMA) and homovanillic acid (HVA) in urine samples. Quantitative data for DOPAC and HVA are presented using 3,4-dihydroxyphenylpropionic acid (DHPPA) as an internal standard.

Electron capture and multiple ion detection of benzodiazepine esters in pharmacokinetic studies

A sensitive and highly specific gas-liquid chromatographic method is described for the determination of benzodiazepine esters. The method involves the extraction of pivoxazepam and 2'-chloropivoxazepam from blood and urine samples and the hydrolysis of both drugs with strong acid to the corresponding 2-amino-5-chlorobenzophenone (ACB) and 2-amino-5,2'-dichlorobenzophenone (ACDB). Recoveries of 97-98% have been obtained and the trifluoroacetic (TFA) derivatives of both benzophenones (ACB-TFA and ACDB-TFA) can be chromatographed on OV-17, in a short time, with good electron-capture detector (ECD) responses. The mass spectra of these derivatives provide abundant molecular ions suitable for mass spectrometric detection by multiple ion detection (MID), with a considerable improvement in specificity compared with the ECD responses. The detection limits in blood specimens have been established at 5-10 ng/ml by ECD and 0.5-0.8 ng/ml by MID. The method has been applied to the study of blood levels attained after i.v. and oral doses in rats and in man.