Chromatography of urinary indole derivatives

Systematic Review on the Metabolic Interest of Glucosinolates and Their Bioactive Derivatives for Human Health

In the last decade, most of the evidence on the clinical benefits of including cruciferous foods in the diet has been focused on the content of glucosinolates (GSL) and their corresponding isothiocyanates (ITC), and mercapturic acid pathway metabolites, based on their capacity to modulate clinical, biochemical, and molecular parameters. The present systematic review summarizes findings of human studies regarding the metabolism and bioavailability of GSL and ITC, providing a comprehensive analysis that will help guide future research studies and facilitate the consultation of the latest advances in this booming and less profusely researched area of GSL for food and health. The literature search was carried out in Scopus, PubMed and the Web of Science, under the criteria of including publications centered on human subjects and the use of Brassicaceae foods in different formulations (including extracts, beverages, and tablets), as significant sources of bioactive compounds, in different types of subjects, and against certain diseases. Twenty-eight human intervention studies met inclusion criteria, which were classified into three groups depending on the dietary source. This review summarizes recent studies that provided interesting contributions, but also uncovered the many potential venues for future research on the benefits of consuming cruciferous foods in our health and well-being. The research will continue to support the inclusion of GSL-rich foods and products for multiple preventive and active programs in nutrition and well-being.

Profiling glucosinolate metabolites in human urine and plasma after broccoli consumption using non-targeted and targeted metabolomic analyses

Broccoli is a popular brassica vegetable and its consumption may decrease the occurrence of cancer in certain populations. To gain insight into the metabolites that may induce physiological responses to broccoli intake, a non-targeted metabolomic approach and a targeted approach for analysis of glucosinolate metabolites were developed using high resolution accurate mass spectrometry. A human study was conducted in which 6 subjects consumed a single meal of 200 g of uncooked broccoli florets. The metabolomic analysis revealed changes in endogenous metabolites and a decrease in hippuric acid after broccoli consumption. Targeted analysis using high-resolution, accurate mass-mass spectrometry (HRAM-MS) enabled detection of low concentrations (nM) of glucosinolate metabolites in human urine and plasma. Glucosinolate metabolites were found in human urine (13) and plasma (8), respectively. Metabolites from methoxyl-indole glucosinolates, arising from broccoli consumption, are reported for the first time. Most glucosinolate metabolites reached their peak concentration in urine 2-4 h after consumption while, in plasma, peak maxima were achieved 2 h after intake. The results suggest that glucoraphanin metabolites (sulforaphane, sulforaphane cysteine, sulforaphane N-acetyl cysteine) and indole metabolites (ascorbigen and methoxyl ascorbigen from indole glucosinolates) may serve as marker compounds for the intake of broccoli.

Role of biomarker tests for diagnosis of neuroendocrine tumours

Neuroendocrine tumours (NETs) are neoplasms that arise from neuroendocrine cells. Neuroendocrine cells and their tumours can secrete a wide range of amines and polypeptide hormones into the systemic circulation. This feature has triggered widespread investigation into circulating biomarkers for the diagnosis of NETs as well as for the prediction of the biological behaviour of tumour cells. Classic examples of circulating biomarkers for gastroenteropancreatic NETs include chromogranin A, neuron-specific enolase and pancreatic polypeptide as well as hormones that elicit clinical syndromes, such as serotonin and its metabolites, insulin, glucagon and gastrin. Biomarker metrics of general markers for diagnosing all gastroenteropancreatic NET subtypes are limited, but specific hormonal measurements can be of diagnostic value in select cases. In the past decade, methods for detecting circulating transcripts and tumour cells have been developed to improve the diagnosis of patients with NETs. Concurrently, modern scanning techniques and superior radiotracers for functional imaging have markedly expanded the options for clinicians dealing with NETs. Here, we review the latest research on biomarkers in the NET field to provide clinicians with a comprehensive overview of relevant diagnostic biomarkers that can be implemented in dedicated situations.

Incidence and prognostic value of serotonin secretion in pancreatic neuroendocrine tumours

BACKGROUND

Serotonin secretion occurs in approximately 1%-4% of patients with a pancreatic neuroendocrine tumour (PNET), but the incidence is not well defined. The aim of this study was to determine the incidence of serotonin secretion with and without carcinoid syndrome and the prognostic value for overall survival (OS).

METHODS

Data were collected from 255 patients with a PNET if 24-hours urinary 5-hydroxyindoleacetic acid excretion (5-HIAA) was assessed. Patients were diagnosed with serotonin secretion if 24-hours urinary 5-HIAA excretion was more than 3× the upper limit of normal (ULN) of 50 μmol/24 hours during follow-up. The effect of serotonin secretion on OS was estimated with uni- and multivariate analyses using a Cox regression.

RESULTS

Two (0.8%) patients were diagnosed with carcinoid syndrome, and another 20 (7.8%) had a serotonin-secreting PNET without symptoms. These patients mostly had ENETS stage IV disease with high chromogranin A (CgA). Serotonin secretion was a negative prognostic factor in univariate analysis (HR 2.2, 95% CI: 1.27-3.81), but in multivariate analysis, only CgA>10× ULN (HR: 1.81, 95% CI: 1.10-2.98) and neuron-specific enolase (NSE) >ULN (HR: 3.51, 95% CI: 2.26-5.46) were predictors for OS. Immunohistochemical staining for serotonin was positive in 28.6% of serotonin-secreting PNETs (one with carcinoid syndrome) and negative in all controls.

CONCLUSION

Carcinoid syndrome is rare in patients with a PNET, but serotonin secretion occurs often. This is a negative prognostic factor for OS, but after correction for CgA and NSE, it is no longer a predictor and probably only a "not-so innocent bystander" in patients with high tumour burden.

Limited value for urinary 5-HIAA excretion as prognostic marker in gastrointestinal neuroendocrine tumours

OBJECTIVE

To determine if urinary 5-hydroxyindoleacetic acid (5-HIAA) excretion is of prognostic value for overall survival (OS) in patients with a gastrointestinal neuroendocrine tumour (NET) and to compare the prognostic value with patient characteristics, ENETS/WHO grading, ENETS TNM staging and biomarkers.

DESIGN AND METHODS

Data was collected from patients with a gastrointestinal NET or a NET with gastrointestinal metastases and available 5-HIAA excretion in 24-h urine samples. Laboratory results were stratified for urinary 5-HIAA and chromogranin A (CgA): <2× upper limit of normal (ULN), 2-10× ULN, or >10× ULN. For neuron-specific enolase (NSE), this was the reference range or >1× ULN. OS was compared using Kaplan-Meier and log-rank tests, and hazard ratios were calculated using Cox regression for univariate and multivariate analyses.

RESULTS

A total of 371 patients were included, 46.6% female with a mean age of 59.9 years. OS was shortest in patients with urinary 5-HIAA excretion >10× ULN vs reference range (median 83 months vs 141 months, P = 0.002). In univariate analysis, urinary 5-HIAA excretion >10× ULN was a negative predictor (HR 1.62, 95% CI: 1.09-2.39). However, in multivariate analysis, only age (HR 1.04, 95% CI: 1.01-1.08), grade 3 disease (HR 5.09, 95% CI: 2.20-11.79), NSE >1× ULN (HR 2.36, 95% CI: 1.34-4.14) and CgA >10× ULN (HR 3.61, 95% CI: 1.56-8.34) remained as the predictors.

CONCLUSION

Urinary 5-HIAA excretion >10× ULN is a negative predictor for OS. However, when added to other biomarkers and grading, it is no longer a predictor for OS. Therefore, it should only be determined to assess carcinoid syndrome and not for prognostic value.

Role of the Gut Microbiome in Uremia: A Potential Therapeutic Target

Also known as the "second human genome," the gut microbiome plays important roles in both the maintenance of health and the pathogenesis of disease. The symbiotic relationship between host and microbiome is disturbed due to the proliferation of dysbiotic bacteria in patients with chronic kidney disease (CKD). Fermentation of protein and amino acids by gut bacteria generates excess amounts of potentially toxic compounds such as ammonia, amines, thiols, phenols, and indoles, but the generation of short-chain fatty acids is reduced. Impaired intestinal barrier function in patients with CKD permits translocation of gut-derived uremic toxins into the systemic circulation, contributing to the progression of CKD, cardiovascular disease, insulin resistance, and protein-energy wasting. The field of microbiome research is still nascent, but is evolving rapidly. Establishing symbiosis to treat uremic syndrome is a novel concept, but if proved effective, it will have a significant impact on the management of patients with CKD.

Determination of urinary 5-hydroxyindoleacetic acid by combining Dμ-SPE using carbon coated TiO2 nanotubes and LC–MS/MS

Background: In this article, carbon coated titanium dioxide nanotubes (TiO2-NT@C) are employed for the determination of 5-hydroxyindole-3-acetic acid in urine by LC–MS/MS. Results: All the variables involved in the extraction have been studied and optimized in depth. The method has been analytically characterized on the basis of its linearity, accuracy, sensitivity and precision. The LOD is 155.8 μg/l while the repeatability and the reproducibility, expressed as RSD, are better than 5.42 and 5.25%, respectively. The obtained relative recovery is 115%. Conclusion: TiO2-NT@C permit the efficient extraction of 5-hydroxyindole-3-acetic acid from complex biological samples such as urine allowing its sensitive determination by LC–MS/MS.

Sensitive profiling of biogenic amines in human urine by capillary electrophoresis with field amplified sample injection

In order to monitor biogenic amines in human urine, a method based on field-amplified sample injection combined with capillary electrophoresis and direct UV absorption detection was developed. Dopamine, tyramine, tryptamine, serotonin and epinephrine were effectively separated and identified in human urine samples, and detection limits were 0.072, 0.010, 0.027, 0.010 and 0.120 µmol/L, respectively. Detection limits comparable to laser-induced fluorescence detection or solid phase extraction combined with capillary electrophoresis were achieved. Parameters affecting electrophoretic system detection sensitivity were investigated. Optimal separation conditions were obtained using as background electrolyte a pH 6.5 mixture of 2-(morpholino)ethanesulfonic acid 20 mmol/L and 30 mmol/L phosphate buffer, containing 0.05% hydroxypropylcellulose and 10% v/v methanol. Injections of the sample solution were performed by applying a voltage of 12 kV for 50 s. Recovery and accuracy ranged between 89.4 and 94.9%, and 89 and 112%, respectively. The method was successfully applied on actual urine samples (from a healthy volunteer): target bioamine content was consistent with endogenous levels reported in the literature. The proposed method is simple, fast and inexpensive and can be conveniently employed in work-related stress studies. The affordability and noninvasive sampling of the method allow epidemiological studies on large number of exposed persons to be performed.

Melatonin: comprehensive profile

This chapter includes the aspects of melatonin. The drug is synthesized in the pineal gland starting from tryptophane or synthetically by using indole as starting material. Melatonin has been used as an adjunct to interleukin-2 therapy for malignant neoplasms, as contraceptive, in the management of various forms of insomnia, to alleviate jet lag following long flights, and finally as free radical scavenger and hence as an antioxidant and an anti-inflammatory. The chapter discusses the drug metabolism and pharmacokinetics and presents various method of analysis of this drug such as biological analysis, spectroscopic analysis, and chromatographic techniques of separation. It also discusses its physical properties such as solubility characteristics, X-ray powder diffraction pattern, and thermal methods of analysis. The chapter is concluded with a discussion on its biological properties such as activity, toxicity, and safety.

5-HIAA excretion is not associated with bone metabolism in carcinoid syndrome patients

In patients with a carcinoid syndrome and neuroendocrine tumors of the digestive tract (carcinoids), elevated circulating serotonin (5-hydroxytryptamine, 5-HT) levels can be demonstrated. It can be hypothesized that bone metabolism will be affected in these patients, since serotonin receptors are expressed on bone cells and serotonin effects on bone have been demonstrated. However, to date, no data are available on bone metabolism parameters in patients with neuroendocrine tumors of the digestive tract (carcinoids). In the current retrospective study we have measured serum bone formation markers P1CP (pro-collagen type I C-terminal), and osteocalcin, and the bone resorption marker NTx (collagen breakdown product N-terminal), in a group of 61 carcinoid patients with increased circulating serotonin levels as demonstrated by increased excretion of the serotonin breakdown product, 5-hydroxy indole acetic acid (5-HIAA), in the urine (>50 μmol/24 h, so-called "hyper-secretors") and a control group of 23 carcinoid patients, without increased 5-HIAA excretion (so-called non-secretors). The 24-h urinary excretion of 5-HIAA reflects the 24-h production of serotonin. Measurements of markers of bone metabolism were performed in serum samples obtained before the start of medical treatment. The hypersecretor group had on average a 10-fold higher urinary 5-HIAA excretion than the control (non-secretor) group. No significant differences in bone metabolism parameters could be demonstrated between hyper-secretors and controls (non-secretors). Correlation and regression analyses could not demonstrate significant age- and sex-adjusted correlations between urinary 5-HIAA excretion and any of the markers for bone turnover. A limitation is that the exposure time to elevated levels of serotonin is unknown, which might have been too short to induce effects on bone metabolism. Treatment of human pre-osteoblasts SV-HFO with serotonin didn't change alkaline phosphatase activity throughout differentiation as well as mineralization. In conclusion, the current study in a unique group of untreated carcinoid patients could not demonstrate a major role for circulating serotonin in the control of bone metabolism.

Uremic solutes from colon microbes

There is renewed interest in identifying organic waste solutes that are normally excreted by the kidneys and must be removed by renal replacement therapy when the kidneys fail. A large number of these waste solutes are produced by colon microbes. Mass spectrometry is expanding our knowledge of their chemical identity, and DNA sequencing technologies are providing new knowledge of the microbes and metabolic pathways by which they are made. There is evidence that the most extensively studied of the colon-derived solutes, indoxyl sulfate and p-cresol sulfate, are toxic. Much more study is required to establish the toxicity of other solutes in this class. Because they are made in an isolated compartment by microbes, their production may prove simpler to suppress than the production of other waste solutes. To the extent that they are toxic, suppressing their production could improve the health of renal failure patients without the need for more intensive or prolonged dialysis.

Micellar electrokinetic capillary chromatography for fast separation and sensitive determination of melatonin and related indoleamines using end-column amperometric detection

MEKC was used in conjunction with end-column amperometric detection (AD) at a carbon disc electrode (0.3 mm diameter) for the selective and sensitive determination of melatonin and its five related indoleamines including its precursors and metabolites in the pineal gland. The introduction of a sample stacking technique in injection and the buffer additive SDS in the buffer solution system provided the rapid and sensitive analysis. Optimal buffer conditions (10 mmol/L phosphate containing 20 mmol/L SDS, pH 7.2), detection potential (+1.0 V vs. Ag/AgCl), and electrokinetic injection 10 s with the separation voltage of 24 kV were employed to achieve the baseline separation of six pineal hormones within 15 min. The peak currents and the analyte concentrations have a good linear relationship over the range of 6.0 x 10(-8) 6.0 x 10(-5 )mol/L. The detection limits for six pineal hormones by AD are 9.7 to 41.8 nmol/L (equal to 2.0 to 9.7 ng/mL) (S/N = 3), respectively. It is proved to provide about 30- to 250-fold improvement over UV, and be comparable with the sensitive fluorescence detection, which needs pre-column derivatization. The proposed method has been applied for analysis of melatonin and related indoleamines in rat pineal glands. A very simple sample pretreatment procedure, merely involving the homogenization step in perchloric acid, was enough to achieve recoveries in the range of 71 to 127% for all the analytes in the pineal gland.

Octreotide exerts only acute, but no sustained, effects on MRI enhancement of liver metastases in carcinoid syndrome

We have investigated the acute and sustained hemodynamic effects of octreotide on hepatic metastases of midgut carcinoids using contrast-enhanced dynamic magnetic resonance imaging (MRI). Seven patients with the carcinoid syndrome and metastasized midgut carcinoid tumors underwent functional dynamic multi-phase gadolinium-enhanced MRI of selected liver metastases at baseline and 60 min after the subcutaneous (s.c.) administration of 100 microg octreotide, and also after 3 months with three times daily (t.i.d.) 100 microg octreotide s.c. Baseline MRIs showed the typical aspect of carcinoid liver metastases with a very bright signal on the T2-weighted sequences and intense enhancement in the arterial phase after injection of gadolinium-diethylenetriaminepentaacetate. MRIs 60 min after the s.c. administration of 100 microg octreotide showed a 34.9 +/- 6.2% (mean +/- SD) reduction in relative enhancement in the selected liver metastases as compared to baseline. In 2 patients, however, there was no (significant) reduction in the relative enhancement in the selected liver metastases 60 min after the s.c. administration of 100 microg octreotide as compared to baseline. Only in 2 patients did the MRIs at 3 months show a decrease in relative enhancement in one of the selected liver metastases. At 3 months, with 100 microg octreotide s.c. t.i.d., there was no correlation between the change in relative enhancement on MRI and the change in 24-hour 5-HIAA excretion. There is thus only an acute effect of octreotide on the perfusion of liver metastases. This study further shows that contrast-enhanced dynamic MRI can be a very useful tool for studying hemodynamic effects of medical therapies on liver metastases in patients with metastatic midgut carcinoids.

Simultaneous Determination of Serotonin and 5-Hydroxyindole-3-acetic Acid in Human Urine by Automated Precolumn Derivatization and Semi-microbore Column Liquid Chromatography with Fluorescence Detection

An improved high-performance liquid-chromatographic (HPLC) assay for the simultaneous determination of serotonin (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA) in human urine is reported. Following the automated precolumn derivatization of urinary 5-HT and 5-HIAA with benzylamine, the derivatives are separated by isocratic elution on a reversed-phase C18 semi-microbore column, and are fluorometrically detected at an excitation wavelength of 345 nm and an emission wavelength of 480 nm. The detection limits of 5-HT and 5-HIAA are 7 and 5 nmol/l in urine (0.7 and 0.5 fmol/20-microl injection). The proposed automatic method permits a highly selective and sensitive determination of 5-HT and 5-HIAA in human urine without any sample purification.

Quantitation of tryptophan, kynurenine and kynurenic acid in human plasma by capillary liquid chromatography-electrospray ionization tandem mass spectrometry

Concentrations of tryptophan and its metabolites in plasma are of great interest in determining proper diagnosis and medication of several neurological diseases like, for example, Alzheimer's disease. A method of standard addition was developed to determine total level of tryptophan and two of its metabolites, kynurenine and kynurenic acid, in human plasma by capillary liquid chromatography-electrospray ionization tandem mass spectrometry. Plasma samples were simply deproteinized by addition of diluted perchloric acid. Samples were then mixed with trichloroacetic acid and injected onto a capillary column. Analytes were separated by a fast gradient elution of the injected samples. Detection was performed by sheathless electrospray tandem mass spectrometry in the multiple reaction monitoring mode. Linear calibration curves were obtained for spiked plasma sample with up to 100% of the expected analytes concentrations. The determined concentrations were well within ranges previously reported (i.e., 6 nM-95 microM) and limit of detections were around 3 nM for each analyte.

Profiling of Tryptophan-related Plasma Indoles in Patients with Carcinoid Tumors by Automated, On-Line, Solid-Phase Extraction and HPLC with Fluorescence Detection

Background: Profiling of the plasma indoles tryptophan, 5-hydroxytryptophan (5-HTP), serotonin, and 5-hydroxyindoleacetic acid (5-HIAA) is useful in the diagnosis and follow-up of patients with carcinoid tumors. We describe an automated method for the profiling of these indoles in protein-containing matrices as well as the plasma indole concentrations in healthy controls and patients with carcinoid tumors.

Methods: Plasma, cerebrospinal fluid, and tissue homogenates were prepurified by automated on-line solid-phase extraction (SPE) in Hysphere Resin SH SPE cartridges containing strong hydrophobic polystyrene resin. Analytes were eluted from the SPE cartridge by column switching. Subsequent separation and detection were performed by reversed-phase HPLC combined with fluorometric detection in a total cycle time of 20 min. We obtained samples from 14 healthy controls and 17 patients with metastasized midgut carcinoid tumors for plasma indole analysis. In the patient group, urinary excretion of 5-HIAA and serotonin was compared with concentrations of plasma indoles.

Results: Within- and between-series CVs for indoles in platelet-rich plasma were 0.6–6.2% and 3.7–12%, respectively. Results for platelet-rich plasma serotonin compared favorably with those obtained by single-component analysis. Plasma 5-HIAA, but not 5-HTP was detectable in 8 of 17 patients with carcinoid tumors. In the patient group, platelet-rich plasma total tryptophan correlated negatively with platelet-rich plasma serotonin (P = 0.021; r = −0.56), urinary 5-HIAA (P = 0.003; r = −0.68), and urinary serotonin (P &lt;0.0001; r = −0.80).

Conclusions: The present chromatographic approach reduces analytical variation and time needed for analysis and gives more detailed information about metabolic deviations in indole metabolism than do manual, single-component analyses.

Determination of uremic toxins in biofluids: creatinine, creatine, uric acid and xanthines

Rapid and accurate determination of small molecule metabolic end-products is vital for clinical diagnosis and study of many metabolic disorders and medical abnormalities. Chromatographic and electrophoretic techniques are attractive for clinical analyses because of the inherent ability to analyze multiple component biofluids and determine the analytes of interest with minimal interference from other species. This manuscript reviews recent (1990-present) developments in chromatography and electrophoresis methodology for the determination of creatinine, creatine, uric acid and xanthines in biofluids.

Clinical chemistry of serotonin and metabolites

Analyses of serotonin and other 5-hydroxyindoles, such as its precursor 5-hydroxytryptophan and major metabolite 5-hydroxyindoleacetic acid (5-HIAA), are indispensable for the elucidation of their (patho)physiological roles. In clinical chemistry attention is mainly focused on the diagnosis and follow-up of carcinoid tumours. For this most laboratories routinely measure urinary 5-HIAA. More recently, measurements of serotonin in platelets and urine have been advocated. Platelet serotonin may be the most sensitive indole marker for the detection of carcinoid tumours that secrete only small amounts of serotonin and/or its precursor 5-hydroxytryptophan. Although several chromatographic techniques have emerged for the analysis of tryptophan-related indoles, HPLC with either electrochemical or fluorometric detection have become the methods of choice for their quantification. HPLC-based methods combine selectivity, sensitivity and high precision, and enable the simultaneous investigation of several metabolically related indoles. This review aims to place the analysis of indoles in biological matrices in a biochemical, physiological and clinical perspective and highlights several important steps in their chromatographic analysis and quantification.

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.

Capillary electrophoresis with laser-induced native fluorescence detection for profiling body fluids

Laser-induced native fluorescence detection with a KrF excimer laser (lambda=248 nm) was used to investigate the capillary electrophoretic (CE) profiles of human urine, saliva and serum without the need for sample derivatization. All separations were carried out in sodium phosphate and/or sodium tetraborate buffers at alkaline pH in a 50-microm I.D. capillary. Sodium dodecyl sulfate was added to the buffer for micellar electrokinetic chromatography (MEKC) analysis of human urine. Although inherently a pulsed source, the KrF excimer laser was operated at a high pulse repetition rate of 553, 1001 or 2009 Hz to simulate a continuous wave excitation source. Detection limits were found to vary with pulse rate, as expected, in proportion to average excitation power. The following detection limits (3sigma) were determined in free solution CE: tryptophan, 4 nM; conalbumin, 10 nM; alpha-lactalbumin, 30 nM. Detection limits for indole-based compounds and catecholamine urinary metabolites under MEKC separation conditions were in the range 7-170 nM.

Ocular melatonin rhythms in the goldfish, Carassius auratus

Ocular melatonin rhythms in the goldfish were studied and compared to those in the pineal organ and plasma. Under light:dark (LD) of 12 h light:12 h dark, melatonin contents in the eye as well as the pineal organ and plasma exhibited clear day-night changes with higher levels at mid-dark than at mid-light. However, melatonin contents in the eye at mid-light and mid-dark were approximately 100 and 9 times greater than those in the pineal organ, respectively. Day-night changes of ocular melatonin persisted after pinealectomy, which abolished those in plasma melatonin under LD 12:12. Ocular melatonin contents in the pinealectomized fish at mid-light were significantly higher than those in the sham-operated control. Under constant darkness (DD), circadian melatonin rhythms were observed in the eye but damped on the 3rd day, whereas plasma melatonin rhythms generated by the pineal organ persisted for at least 3 days. Under constant light, ocular melatonin contents exhibited a significant fluctuation with a smaller amplitude than that under DD, whereas plasma melatonin remained at low levels. These results indicate the involvement of LD cycles, a circadian clock, and the pineal organ in the regulation of ocular melatonin rhythms in the goldfish.

High-performance liquid chromatographic profiling of indolylacryloylglycine and its possible precursors in body fluids

Indolylacryloylglycine (IAcrGly) is one of the physiological components of urine, although its source and its role in the human organism have not yet been unambiguously established. Changes in the IAcrGly excretion level have been found under some physiological (age dependence, seasonal variations) and pathological (photodermatoses, muscle dystrophy, liver cirrhosis) conditions. The proposed method for IAcrGly, indolylacrylic acid and its possible precursors, namely indolyllactic and indolylpropionic acids, involves deproteinization and extraction of urine on a Sep Pak C18 cartridge. HPLC analysis was carried out using a DataApex liquid chromatograph, equipped with an LCD 2082 UV detector, signals being acquired with a CSW workstation. The chromatographic column was Spherisorb ODS, 5 microns (125 x 4 mm I.D.), the mobile phase for isocratic elution was ethanol-1% acetic acid (27:73) and the flow-rate was 0.7 ml/min. The lower response limit is about 1 mumol/l for all metabolites at 280 nm.

Separation of tryptophan and related indoles by micellar electrokinetic chromatography with KrF laser-induced fluorescence detection

Micellar electrokinetic chromatography (MEKC) was applied for the separation of tryptophan and related indoles. Using a 5 mM sodium borate buffer (pH 9.2) containing 50 mM sodium dodecyl sulfate and 5% acetonitrile, eleven indoles were baseline separated in under 17 min. Most of the indoles were detected at the nM level by native fluorescence using KrF laser-induced fluorescence (LIF), which was approximately 100 times more sensitive than UV absorption detection at 200 nm. Preliminary results show that the MEKC-LIF with direct sample injection is a feasible method for assessing indole profiles in diluted urine and serum.

Modification of a tunable UV-visible capillary electrophoresis detector for simultaneous absorbance and fluorescence detection: profiling of body fluids for drugs and endogenous compounds

Using fused-silica optical fibres for fluorescence light collection and bandpass filters for selection of emission wavelengths, a capillary electrophoresis detection cell of a conventional, tunable UV-Vis absorbance detector was adapted for simultaneous fluorescence (at selected emission wavelength) and absorbance (at selected excitation wavelength) detection. Detector performance is demonstrated with the monitoring of underivatized fluorescent compounds in body fluids by micellar electrokinetic capillary chromatography with direct sample injection. Compared with UV absorption detection, fluorescence detection is shown to provide increased selectivity and for selected compounds also up to tenfold higher sensitivity. Examples studied include screening for urinary indole derivatives (tryptophan, 5-hydroxytryptophan, tyrosine, 3-indoxyl sulfate and 5-hydroxyindole-3-acetic acid) and catecholamine metabolites (homovanillic acid and vanillylmandelic acid) and the monitoring of naproxen in serum, quinidine in serum and urine and of salicylate and its metabolites in serum and urine.

Regional 5-hydroxyindoleacetic acid production in humans

Veno-arterial plasma concentration differences and regional organ plasma flows were used to quantify the relative amounts of 5-hydroxyindoleacetic acid (5-HIAA) contributed by various sites into the peripheral circulation. Positive venoarterial concentration gradients were found in the hepatosplanchnic, forearm, cardiac and jugular vessels in the healthy subjects. The renal circulation was determined to be the principal site of 5-HIAA clearance, extracting 18 +/- 2 nmol/min. The gut was the greatest contributor to the total 5-HIAA plasma pool with the relative contributions of the various organs being as follows: hepatosplanchnic organs 58%, skeletal muscle 26%, brain 6% and the heart 3%. The source of 5-HIAA stemming from these regional beds remains unknown, it may derive from serotonin taken up by and deaminated in ubiquitous endothelial cells, enterochromaffin cells of the gut, peripheral serotonergic nerves, serotonin turnover in platelets or perhaps the metabolism of serotonin taken up by sympathetic nerves. To test the latter hypothesis we examined 23 patients with chronic congestive heart failure and 9 patients with pure autonomic failure to investigate the possible effects of sympathetic nervous system overactivity and underactivity on peripheral 5-HIAA production and plasma 5-HIAA concentration. The resting arterial plasma 5-HIAA concentration in the heart failure patients was increased three-fold. This elevated plasma 5-HIAA concentration was attributable to an increased rate of whole body 5-HIAA production. The arterial 5-HIAA plasma concentration in the autonomic failure patients was paradoxically elevated, being 70% greater than that of the healthy subjects. The increased 5-HIAA plasma concentration in these patients was accounted for by a reduction in 5-HIAA plasma clearance. In all subjects studied there was a weak relationship only between total body norepinephrine spillover to plasma and the arterial 5-HIAA plasma concentration. We found that in healthy subjects the overflow of 5-HIAA into the hepatic vein was significantly related to the underlying degree of sympathetic activity. It can be concluded that 5-HIAA is produced at a number of sites throughout the body with the arterial plasma concentration being dependent on both the level of production and plasma clearance. By far the majority of 5-HIAA in plasma is derived from the gut with only minimal contribution from the brain.

Monoaminergic neuronal activity in subcortical brain regions in essential hypertension

In this study we aimed to elucidate the role of central noradrenergic, dopaminergic, adrenergic and serotonergic neuronal systems in the development of essential hypertension. Fifteen untreated essential hypertensive subjects (aged 44 +/- 3 years) and 32 healthy volunteers (aged 38 +/- 3 years) participated in this study. By combining direct blood sampling techniques with cerebral blood flow scans we were able to differentiate between cortical and subcortical venous drainage of the brain. Veno-arterial MHPG, HVA and 5-HIAA plasma concentration gradients combined with internal jugular vein plasma flows were used, according to the Fick Principle, to derive metabolite spillovers which in turn were used as indicators of central noradrenergic, dopaminergic and serotonergic neuronal activity, respectively. These amine systems, in both the brainstem and forebrain, have been implicated in the regulation of sympathetic outflow and blood pressure. Total body noradrenaline spillover to plasma was concurrently measured to assess the relationship between central monoamine turnover and sympathetic activity. Compared to their healthy counterparts the hypertensive subjects had an elevated release of MHPG from subcortical brain regions (1.4 +/- 0.3 v 0.5 +/- 0.2 nmol/min, p < 0.05). An inverse relationship between blood pressure and subcortical HVA overflow existed, with the HVA overflow being significantly lower in the hypertensives (0.5 +/- 0.2 v 2.1 +/- 0.5 nmol/min, p < 0.05). Subcortical 5-HUAA overflow did not differ between the two groups, and adrenaline spillover from the brain was not detected in either group. Subcortical MHPG overflow was significantly correlated with total body NA spillover to plasma (p < 0.05). These results indicate that reciprocal aberrations in subcortical noradrenaline and dopamine turnover exist in essential hypertension. Although the physiological significance of this remains to be unequivocally elucidated we postulate that elevated subcortical noradrenergic activity, presumably in the forebrain where noradrenergic neurons are pressor, may cause sympathoexcitation and play a role in the development of essential hypertension.

High performance liquid chromatographic profiling of tryptophan and related indoles in body fluids and tissues of carcinoid patients

A high performance liquid chromatographic method with quaternary gradient elution and fluorometric detection was developed for profiling of tryptophan (TRP), 5-hydroxytryptophan, serotonin (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA) in urine, platelet-rich plasma and (tumour) tissue of patients with carcinoid tumours. Prior to injection, urine samples were diluted and filtered. Platelet-rich plasma and tissue homogenates were prepurified by C18 solid phase extraction. Detection limits were approx. 2 pmol. Results of urinary 5-HT and 5-HIAA compared favourably with those of single component analyses. No consistent diurnal variations were found for TRP, 5-HT and 5-HIAA in 12-h urine samples from 15 healthy adults. Abstinence of 5-HT-rich foods reduced urinary levels of 5-HT and 5-HIAA. C18 extraction of indoles from protein-containing matrices was studied in platelet-rich plasma. Although time-consuming and complicated for daily routine use, the present approach offers particular advantages over single component analyses in the study of TRP metabolism in patients with carcinoid tumours.

The determination of 5-hydroxytryptamine, related indolealkylamines and 5-hydroxyindoleacetic acid in the bovine eye by gas chromatography-negative ion chemical ionization mass spectrometry

Methods were developed for the analysis of 5-hydroxytryptamine, related indolealkylamines (tryptamine, melatonin, 5-methoxytryptamine, N-acetyl-5-hydroxytryptamine and 6-hydroxymelatonin) and 5-hydroxyindole-3-acetic acid (5HIAA) in bovine retina, aqueous and vitreous humours. 5-Hydroxytryptamine and related indolealkylamines were extracted and derivatized to form their corresponding pentafluoropropionyl spirocyclic derivatives. 5HIAA was extracted and derivatized to the corresponding pentafluoropropionamide-trifluoroethyl derivative. Identification and quantitation by gas chromatography-negative ion chemical ionization mass spectrometry was made with reference to deuteriated internal standards. 5-Hydroxytryptamine was present in all (n = 34) retinal samples analysed (20.53 +/- 1.64 ng) while N-acetyl-5-hydroxytryptamine was detected in half of the samples of retina (0.06 +/- 0.02 ng). Melatonin (0.15 +/- 0.06 ng) and tryptamine (0.78 +/- 0.34 ng) were detected in only a small number of retinas. 5-Methoxytryptamine was not present in retina. 5-Hydroxytryptamine was also present in aqueous (0.76 +/- 0.17 ng ml-1 and vitreous (0.35 +/- 0.05 ng ml-1' humours from bovine eye. Tryptamine, melatonin, 5-methoxytryptamine and N-acetyl-5-hydroxytryptamine were not detected in bovine aqueous and vitreous humours. 5HIAA was found in both bovine aqueous (2.03 +/- 0.38 ng ml-1) and vitreous (0.65 +/- 0.06 ng ml-1) humours, but its consistent determination in retina was obviated by interference from spurious peaks.

Indolic urinary melanogens: separation and identification by gas chromatography with selected-ion monitoring mass spectrometry of 5-hydroxy-6-methoxyindole-2-carboxylic and 5-methoxy-6-hydroxyindole-2- carboxylic acids

Two isomeric urinary melanogens, 5-hydroxy-6-methoxyindole-2-carboxylic acid and 5-methoxy-6-hydroxyindole-2-carboxylic acid, have been separated by gas chromatography with selected-ion monitoring mass spectrometry. After chemical synthesis of one of these two isomers, 5-methoxy-6-hydroxyindole-2-carboxylic acid, and the establishment of the mass spectrum of its trimethylsilylated derivative, a 30-ml sample of a melanotic 24-h urine was adjusted to pH 1 and extracted twice with 10 ml of ethyl acetate. The extract was evaporated to dryness and the residue derivatized with methyl-8, followed by Tri-Sil/TBT. Silylated derivatives were analysed by gas chromatography with selected-ion monitoring mass spectrometry. The mass spectrum of the 5-methoxy-6-hydroxyindole-2-carboxylic acid allowed the determination of the retention times of both isomers.

Chromatographic methods for the analysis of basic neurotransmitters and their acidic metabolites

Chromatographic techniques for the determination of trace amounts of neurotransmitters were reviewed. The two techniques found to be most useful were GC-MS and the reversed-phase mode of HPLC with an electrochemical or fluorescent detector. For structure determination or unequivocal peak identification, GC-MS is the method of choice. In addition the limits of detection of GC-MS were better than those obtained by HPLC. However for routine analyses, HPLC is now being used in studies of mental illness and other diseases. Good resolution, reproducibility and sensitivity can be obtained without the derivatisation steps required for GC-MS, and catecholamines, serotonin, and their acidic metabolites can be concomitantly determined in one analysis.

High performance liquid chromatographic analysis of time-dependent changes in urinary excretion of indoleamines following tryptophan administration

Analytical conditions of prepurification extraction and HPLC separation were optimized for determination of urinary serotonin and tryptamine. Under optimal conditions, serotonin, tryptamine and an internal standard were extracted with 15% v/v n-propanol in diethyl ether from urine samples alkalized with a phosphate buffer (0.75 mol/L, pH 10.0), and then they were re-extracted into an HCl solution (0.1 mol/L). Purified indoleamines were simultaneously separated by reversed-phase ion-pair HPLC with native fluorescence detection. Urinary serotonin and tryptamine were selectively determined within about 45 min per sample for the whole procedure. Analytical recovery, reproducibility and detection sensitivity were satisfactory for pursuing time-dependent changes in indoleamine levels. Urinary excretion profiles of serotonin and tryptamine in subjects dosed with L-tryptophan were successfully analyzed by our method.