Determination of dopamine-3- and 4-O-sulphate in human plasma and urine by anion-exchange high-performance liquid chromatography with fluorimetric detection

Development of an HPLC-MS/MS Method for Chiral Separation and Quantitation of (R)- and (S)-Salbutamol and Their Sulfoconjugated Metabolites in Urine to Investigate Stereoselective Sulfonation

The aim of this study was to develop and optimize a chiral HPLC-MS/MS method for quantitative analysis of (R)-/(S)-salbutamol and (R)-/(S)-salbutamol-4'-O-sulfate in human urine to allow for bioanalytical quantitation of the targeted analytes and investigations of stereoselectivity in the sulfonation pathway of human phase Ⅱ metabolism. For analytical method development, a systematic screening of columns and mobile phases to develop a separation via enantiomerically selective high performance liquid chromatography was performed. Electrospray ionization settings were optimized via multiple-step screening and a full factorial design-of-experiment. Both approaches were performed matrix-assisted and the predicted values were compared. The full factorial design was superior in terms of prediction power and knowledge generation. Performing a longitudinal excretion study in one healthy volunteer allowed for the calculation of excretion rates for all four targeted analytes. For this proof-of-concept, either racemic salbutamol or enantiopure levosalbutamol was administered perorally or via inhalation, respectively. A strong preference for sulfonation of (R)-salbutamol for inhalation and peroral application was found in in vivo experiments. In previous studies phenol sulfotransferase 1A3 was described to be mainly responsible for salbutamol sulfonation in humans. Thus, in vitro and in silico investigations of the stereoselectivity of sulfotransferase 1A3 complemented the study and confirmed these findings.

Biomarkers of intake for tropical fruits

Consumption of fruit and vegetable is a key component of a healthy and sustainable diet. However, their accurate dietary assessment remains a challenge. Due to errors in self-reporting methods, the available dietary information is usually biased. Biomarkers of intake constitute objective tools to better reflect the usual or recent consumption of different foods, including fruits and vegetables. Partners of The Food Biomarker Alliance (FoodBall) Project have undertaken the task of reviewing the available literature on putative biomarkers of tropical fruit intake. The identified candidate biomarkers were subject to validation evaluation using eight biological and chemical criteria. This publication presents the current knowledge on intake biomarkers for 17 tropical fruits including banana, mango, and avocado as the most widely consumed ones. Candidate biomarkers were found only for banana, avocado, and watermelon. An array of banana-derived metabolites has been reported in human biofluids, among which 5-hydroxyindole-acetic acid, dopamine sulfate, methoxyeugenol glucuronide, salsolinol sulfate, 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-β-carboline-sulfate, and other catecholamine metabolites. Their validation is still at an early stage, with insufficient data on dose-response relationship. Perseitol and mannoheptulose have recently been reported as candidate biomarkers for avocado intake, while the amino acid citrulline has been associated with watermelon intake. Additionally, the examination of food composition data revealed some highly specific phytochemicals, which metabolites after absorption may be further studied as putative BFI for one or several tropical fruits. To make the field move forward, untargeted metabolomics, as a data-driven explorative approach, will have to be applied in both intervention and observational studies to discover putative BFIs, while their full validation and the establishment of dose-response calibration curves will require quantification methods at a later stage.

Allosteres to regulate neurotransmitter sulfonation

Catecholamine neurotransmitter levels in the synapses of the brain shape human disposition-cognitive flexibility, aggression, depression, and reward seeking-and manipulating these levels is a major objective of the pharmaceutical industry. Certain neurotransmitters are extensively sulfonated and inactivated by human sulfotransferase 1A3 (SULT1A3). To our knowledge, sulfonation as a therapeutic means of regulating transmitter activity has not been explored. Here, we describe the discovery of a SULT1A3 allosteric site that can be used to inhibit the enzyme. The structure of the new site is determined using spin-label-triangulation NMR. The site forms a cleft at the edge of a conserved ∼30-residue active-site cap that must open and close during the catalytic cycle. Allosteres anchor into the site via π-stacking interactions with two residues that sandwich the planar core of the allostere and inhibit the enzyme through cap-stabilizing interactions with substituents attached to the core. Changes in cap free energy were calculated ab initio as a function of core substituents and used to design and synthesize a series of inhibitors intended to progressively stabilize the cap and slow turnover. The inhibitors bound tightly (34 nm to 7.4 μm) and exhibited progressive inhibition. The cap-stabilizing effects of the inhibitors were experimentally determined and agreed remarkably well with the theoretical predictions. These studies establish a reliable heuristic for the design of SULT1A3 allosteric inhibitors and demonstrate that the free-energy changes of a small, dynamic loop that is critical for SULT substrate selection and turnover can be calculated accurately.

Determination of Serotonin and Dopamine Metabolites in Human Brain Microdialysis and Cerebrospinal Fluid Samples by UPLC-MS/MS: Discovery of Intact Glucuronide and Sulfate Conjugates

An UPLC-MS/MS method was developed for the determination of serotonin (5-HT), dopamine (DA), their phase I metabolites 5-HIAA, DOPAC and HVA, and their sulfate and glucuronide conjugates in human brain microdialysis samples obtained from two patients with acute brain injuries, ventricular cerebrospinal fluid (CSF) samples obtained from four patients with obstructive hydrocephalus, and a lumbar CSF sample pooled mainly from patients undergoing spinal anesthesia in preparation for orthopedic surgery. The method was validated by determining the limits of detection and quantification, linearity, repeatability and specificity. The direct method enabled the analysis of the intact phase II metabolites of 5-HT and DA, without hydrolysis of the conjugates. The method also enabled the analysis of the regioisomers of the conjugates, and several intact glucuronide and sulfate conjugates were identified and quantified for the first time in the human brain microdialysis and CSF samples. We were able to show the presence of 5-HIAA sulfate, and that dopamine-3-O-sulfate predominates over dopamine-4-O-sulfate in the human brain. The quantitative results suggest that sulfonation is a more important phase II metabolism pathway than glucuronidation in the human brain.

Hydroxylated serotonin and dopamine as substrates and inhibitors for human cytosolic SULT1A3

Sulfation as catalyzed by the cytosolic sulfotransferases (SULTs) is known to play an important role in the regulation and homeostasis of monoamine neurotransmitters. The current study was designed to examine the occurrence of the sulfation of 7-hydroxyserotonin and 6-hydroxydopamine by human cytosolic SULTs and to investigate the inhibitory effects of these hydroxylated derivatives on the sulfation of their unhydroxylated counterparts, serotonin and dopamine. A systematic study using 11 known human cytosolic SULTs revealed SULT1A3 as the responsible enzyme for the sulfation of 7-hydroxyserotonin and 6-hydroxydopamine. The pH-dependence and kinetic constants of SULT1A3 with 7-hydroxyserotonin or 6-hydroxydopamine as substrate were determined. The inhibitory effects of 7-hydroxyserotonin and 6-hydroxydopamine on the sulfation of serotonin and dopamine were evaluated. Kinetic analyses indicated that the mechanism underlying the inhibition by these hydroxylated monoamine derivatives is of a competitive-type. Metabolic labeling experiments showed the generation and release of [(35) S]sulfated 7-hydroxyserotonin and [(35) S]sulfated 6-hydroxydopamine when SK-N-MC human neuroblastoma cells were labeled with [(35) S]sulfate in the presence of 7-hydroxyserotonin or 6-hydroxydopamine. Upon transfection of the cells with siRNAs targeted at SULT1A3, diminishment of the SULT1A3 protein and concomitantly the sulfating activity toward these hydroxylated monoamines was observed. Taken together, these results indicated clearly the involvement of sulfation in the metabolism of 7-hydroxyserotonin and 6-hydroxydopamine. By serving as substrates for SULT1A3, these hydroxylated monoamines may interfere with the homeostasis of endogenous serotonin and dopamine.

A versatile polyacrylamide gel electrophoresis based sulfotransferase assay

Background

Sulfotransferases are a large group of enzymes that regulate the biological activity or availability of a wide spectrum of substrates through sulfation with the sulfur donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS). These enzymes are known to be difficult to assay. A convenient assay is needed in order to better understand these enzymes.

Results

A universal sulfotransferase assay method based on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) is described. This assay has been successfully applied to substrates as small as α-naphthol and as big as proteoglycans. As examples, we present the assays for recombinant human CHST4, TPST1, CHST3 and HS6ST1. In order to assess whether a small molecule can be applicable to this type of assay, a method to estimate the relative mobility of a molecule to PAPS is also presented. The estimated relative mobilities of various sulfated small molecules generated by SULT1A1, SULT1E1, SULT2A1 and CHST4 are in the range of ± 0.2 of the actual relative mobilities.

Conclusion

The versatility of the current method comes from the ability that SDS-PAGE can separate proteins and small molecules according to different parameters. While mobilities of proteins during SDS-PAGE are inversely related to their sizes, mobilities of small molecules are positively related to their charge/mass ratios. The predicted relative mobility of a product to PAPS is a good indicator of whether a sulfotransferase can be assayed with SDS-PAGE. Because phosphorylation is most similar to sulfation in chemistry, the method is likely to be applicable to kinases as well.

Regioselective sulfonation of dopamine by SULT1A3 in vitro provides a molecular explanation for the preponderance of dopamine-3-O-sulfate in human blood circulation

SULT1A3 is an enzyme that catalyzes the sulfonation of many endogenous and exogenous phenols and catechols. The most important endogenous substrate is dopamine (DA), which is often used as a probe substrate for SULT1A3. We developed a new method for analyzing the SULT1A3 reaction products by high-performance liquid chromatography (HPLC) with electrochemical detection. The sulfonate donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS), DA and the two dopamine sulfates, DA-3-O-sulfate and DA-4-O-sulfate, can be separated within 3 min. This enables quantitation of the sulfates without radioactive PAPS or the precipitation of unreacted PAPS. Both sulfates were synthesized as reference substances and characterized by (1)H and (13)C nuclear magnetic resonance (NMR), mass spectrometry (MS) and tandem mass spectrometry (MS/MS). The purity of the dopamine sulfates was estimated by HPLC using a diode array detector. We determined the enzyme kinetic parameters for formation of DA-3-O-sulfate and DA-4-O-sulfate using purified recombinant human SULT1A3. The reactions followed Michaelis-Menten kinetics up to 50 microM DA concentration, and strong substrate inhibition was observed at higher concentrations. The apparent K(m) values for sulfonation at both hydroxy groups were similar (2.21+/-0.764 and 2.59+/-1.06 microM for DA-4-O-sulfate and DA-3-O-sulfate, respectively), but the V(max) was approximately six times higher for the formation of the 3-O-sulfate (344+/-139 nmol/min/mg protein) than the 4-O-sulfate (45.4+/-16.5 nmol/min/mg protein). These results are in accordance with the observation that DA-3-O-sulfate is more abundant in human blood than DA-4-O-sulfate and that in the crystal structure of SULT1A3 with dopamine bound to the active site, the 3-hydroxy group is aligned to form hydrogen bonds with catalytic residues of the enzyme.

Sulfonation and molecular action

The sulfonation of endogenous molecules is a pervasive biological phenomenon that is not always easily understood, and although it is increasingly recognized as a function of fundamental importance, there remain areas in which significant cognizance is still lacking or at most minimal. This is particularly true in the field of endocrinology, in which the sulfoconjugation of hormones is a widespread occurrence that is only partially, if at all, appreciated. In the realm of steroid/sterol sulfoconjugation, the discovery of a novel gene that utilizes an alternative exon 1 to encode for two sulfotransferase isoforms, one of which sulfonates cholesterol and the other pregnenolone, has been an important advance. This is significant because cholesterol sulfate plays a crucial role in physiological systems such as keratinocyte differentiation and development of the skin barrier, and pregnenolone sulfate is now acknowledged as an important neurosteroid. The sulfonation of thyroglobulin and thyroid hormones has been extensively investigated and, although this transformation is better understood, there remain areas of incomplete comprehension. The sulfonation of catecholamines is a prevalent modification that has been extensively studied but, unfortunately, remains poorly understood. The sulfonation of pituitary glycoprotein hormones, especially LH and TSH, does not affect binding to their cognate receptors; however, sulfonation does play an important role in their plasma clearance, which indirectly has a significant effect on biological activity. On the other hand, the sulfonation of distinct neuroendocrine peptides does have a profound influence on receptor binding and, thus, a direct effect on biological activity. The sulfonation of specific extracellular structures plays an essential role in the binding and signaling of a large family of extracellular growth factors. In summary, sulfonation is a ubiquitous posttranslational modification of hormones and extracellular components that can lead to dramatic structural changes in affected molecules, the biological significance of which is now beginning to be appreciated.

Determination of urinary vanillactic acid and plasma dihydroxyphenylalanine as markers of non-secreting neuroblastoma by high-performance liquid chromatography with electrochemical detection

An accurate and precise isocratic high-performance liquid chromatographic technique for the analysis of urinary vanillactic acid (VLA) and plasma dihydroxyphenylalanine (DOPA), especially at low concentrations (pmol/l) for VLA and nmol/l for DOPA), is described. The compounds were purified in a single step, (on an anion exchanger for VLA and on aluminium oxide for DOPA), separated by ion-pair reversed-phase liquid chromatography, and detected electrochemically. A single analysis was complete within 18 min. Mean recoveries of 103 and 81% were obtained for VLA and DOPA, respectively, and the limits of detection were 42 and 76 pmol/l, respectively. The mean values of the intra-assay coefficient of variation were 14 and 7.1% for VLA and DOPA, respectively, and the mean values of the inter-assay coefficient of variation were 15.7 and 11.6%, respectively. Modifications of the retention times (between 2 and 42 min) induced by changes in the eluent were determined. Reference values for normal children and children with neuroblastoma or various tumours are given.

New rapid analysis method demonstrates differences in 6-[18F] fluoro-L-dopa plasma input curves with and without carbidopa and in hemi-MPTP lesioned monkeys

Kinetic modeling of the PET tracer 6-[18F]fluoro-L-dopa ([18F]Dopa), used to measure presynaptic dopamine function, requires the accurate determination of the plasma input curve. We have developed a new method that uses alumina extraction preceded by cation and anion exchange resins to determine the parent compound, [18F]Dopa and its critical metabolite 3-O-methyl-6-[18F]fluoro-L-dopa. Using this method we found that carbidopa increases the plasma input of [18F]Dopa while decreasing the rate of metabolite formation, and that previous drug treatment can significantly effect [18F]Dopa metabolism.

Urinary dopamine sulfate: regulations and significance in neurological disorders

Dopamine-3-O-sulfate (DA-3-O-S) and dopamine-4-O-sulfate (DA-4-O-S) are important end products of L-dopa metabolism. Therefore they may give indications of disturbances in the peripheral metabolism of catecholamines, when measured in urine samples of patients with Parkinson's disease (PD). In addition, information about the reliability of DA sulfatation after L-dopa therapy may be of significance for its role in the elimination of DA from the peripheral nervous system. Although DA-3-O-S appears to be the predominant sulfo-conjugate in urine, there are no changes in PD nor in depression syndrome compared to controls with or without other neurological disorders. By contrast, DA-4-O-S is significantly decreased in de novo PD subjects. However, a similar reduction is notable in patients with other neurological disorders. In depressed persons the loss of this compound was less pronounced as compared to de novo PD. Treatment with combined L-dopa therapy caused increased excretion of DA-3-O-S, while changes in DA-4-O-S were only marginal. It is concluded that urinary DA-3-O-S cannot be used as marker for PD, while DA-4-O-S is significantly reduced in a variety of neurological disorders and in particular in de novo PD. Further studies are necessary to elucidate its role as possible peripheral marker to distinguish preclinical PD and depression syndrome.

Contents of dopamine sulfoconjugate isomers and their desulfation in dog arteries

In humans and dogs, the plasma contains little free dopamine, and dopamine is almost all present in two isomeric forms of conjugates with sulfate esters, dopamine-3-O-sulfate and dopamine 4-O-sulfate. These two isomers differ in metabolic stability and biological activity. The physiological role of dopamine sulfates is controversial. In the present study on dogs, noradrenaline, dopamine and the two dopamine sulfate isomers in the peripheral arteries were measured by high-performance liquid chromatography, and the possibility that dopamine sulfate isomers are deconjugated in the arteries as a source of free dopamine was examined. The arteries were found to contain free dopamine and dopamine 3-O-sulfate at concentrations of 0.09-0.54 and 0.008-0.015 pmol/mg wet tissue, respectively. No dopamine 4-O-sulfate was found in the arteries or the plasma. Arylsulfatase activity was assayed by incubating a crude extract of arterial homogenate with dopamine 3-O-sulfate or dopamine 4-O-sulfate and measuring the dopamine produced. Exogenous dopamine 4-O-sulfate was desulfated by the extract, but dopamine 3-O-sulfate, which is the predominant isomer in the artery, was not desulfated by the extract. These results suggest that dopamine sulfate is not converted to dopamine in physiological conditions in the dog.

Biogenic amines and their metabolites in body fluids of normal, psychiatric and neurological subjects

The biogenic monoamines and their metabolites have been isolated, identified and quantified in human body fluids over the past forty years using a wide variety of chromatographic separation and detection techniques. This review summarizes the results of those studies on normal, psychiatric and neurological subjects. Tables of normal values and the methods used to obtain them should prove to be useful as a reference source for benchmark amine and metabolite concentrations and for successful analytical procedures for their chromatographic separation, detection and quantification. Summaries of the often contradictory results of the application of these methods to psychiatric and neurological problems are presented and may assist in the assessment of the validity of the results of experiments in this field. Finally, the individual, environmental and the methodological factors affecting the concentrations of the amines and their metabolites are discussed.

Preparation of dopamine 3-O-sulphate and dopamine 4-O-sulphate as reference substances and high-performance liquid chromatographic trace determination

Simple syntheses of the biologically important but hitherto difficult to obtain dopamine sulpho conjugates dopamine 3-O-sulphate (I) and dopamine 4-O-sulphate (II), as analytical reference substances, starting from dopamine hydrochloride are described. A method for the determination of I and II with reversed-phase high-performance liquid chromatographic separation and coulometric detection in human urine together with calibration and current-voltage curves are presented. Detection limits of approximately 100 pg of I or II and unequivocal substance identifications even in very complex substrates such as human urine are reported.

Plasma levels and renal clearance of two isomers of dopamine sulfate in patients with essential hypertension

Two isomers of dopamine sulfate, dopamine 3-O-sulfate(3-O-S) and dopamine 4-O-sulfate(4-O-S), in the plasma and urine of patients with essential hypertension and normotensive controls were measured by HPLC-fluorometry. The plasma level of 3-O-S was significantly higher in patients with essential hypertension than in normotensive controls (20.9 +/- 2.2 pmol/ml and 16.3 +/- 1.4 pmol/ml respectively, p less than 0.05) and the plasma levels of 4-O-S were slightly increased in hypertensive patients. The plasma level of 3-O-S was correlated with the serum level of creatinine in both normotensives and hypertensives. In hypertensives, the plasma level of 3-O-S was also correlated with that of noradrenaline. However the creatinine clearances were similar in the two groups, the urinary clearance of 3-O-S was slightly lower in patients with essential hypertension than in normotensive controls. These data indicate that the plasma level of 3-O-S is elevated in essential hypertension because of the abnormality in dopaminergic metabolism and renal disturbance in its excretion.

Effects of oral and intravenous administrations of dopamine and L-dopa on plasma levels of two isomers of dopamine sulfate in man

The levels of two isomers of dopamine sulfate, dopamine-3-O-sulfate (DA3S) and dopamine-4-O-sulfate (DA4S), in human plasma were measured by HPLC-fluorometry. The basal plasma levels of DA3S and DA4S in the early morning were 13.8 +/- 1.9 and 3.2 +/- 0.5 pmoles/ml, respectively (means +/- S.E.M.). Oral administrations of dopamine (50 mg/body) and 1-dihydroxyphenylalanine (L-DOPA, 250 mg/body) increased the plasma levels of these dopamine sulfates almost 100-fold to 1807 +/- 266 and 1674 +/- 195 pmoles/ml of DA3S, and 466 +/- 83 and 321 +/- 76 pmoles/ml of DA4S. Intravenous dopamine infusion (5 micrograms/kg/min for 30 min) markedly increased the plasma free dopamine concentration, as expected, but increased the levels of DA3S and DA4S only slightly to 110 +/- 32 and 25 +/- 9 pmoles/ml, respectively. In contrast, intravenous L-DOPA (25 mg/body) resulted in a slight increase of free dopamine followed by marked increases of DA3S and DA4S to 691 +/- 219 and 139 +/- 40 pmoles/ml, respectively. These data indicate that O-sulfation of dopamine, especially 3-O-sulfation, is the main pathway for metabolism of intravenously and orally administered L-DOPA and orally ingested dopamine. This sulfation is suggested to occur in the gut wall.

Effects of administration of dopamine and L-DOPA to dogs on their plasma level of dopamine sulfate

The effect of intravenous administration of dopamine (DA) or L-3,4-dihydroxyphenylalanine (L-DOPA), its immediate precursor, on the level of DA sulfate in dog plasma was examined, to clarify the source and physiological significance of DA sulfate which is present at high level in the plasma. After DA administration, the plasma level of free DA increased markedly, but the level of DA sulfate did not change. However, after administration of L-DOPA, the levels of both free DA and DA sulfate increased greatly. After a single injection of L-DOPA, increase in the level of free DA was transient, but that of DA sulfate persisted for a long time. These results suggest that some of the DA sulfate in dog plasma is formed from circulating L-DOPA, not from circulating DA, and that formation of DA conjugate may play a role in regulating the plasma level of free DA.

Direct measurement of dopamine O-sulfate in plasma and cerebrospinal fluid

This paper describes a method for measurement of dopamine 3-O-sulfate (DA3S) and dopamine 4-O-sulfate (DA4S) in dog and human plasma and dog cerebrospinal fluid. C18 solid-phase extraction columns were utilized for sample preparation. DA3S and DA4S were separated by high-performance liquid chromatography and then quantified by dual-electrode electrochemical detection. [3H]Dopamine O-sulfate (DAS) was used as internal standard. Recovery of authentic DAS added to dog plasma and carried through the entire procedure was 49.9 +/- 6.3% for DA3S (n = 9) and 42.2 +/- 4.3% for DA4S (n = 8). The lower limit of detection (signal-to-noise ratio of 3) was 20 fmol for each DAS isomer. The within-assay coefficient of variation for DA3S in dog plasma averaged 5.8% (range 2.0-12%, n = 5). The between-assay coefficient of variation for DA3S in dog plasma was 3.8% (n = 3). DAS levels in plasma of conscious dogs were 20.3 +/- 6.9 pmol/ml DA3S and 5.91 +/- 3.5 pmol/ml DA4S (n = 5). Cerebrospinal fluid levels were 3.06 +/- 3.22 pmol/ml DA3S and 0.10 +/- 0.18 pmol/ml DA4S in dogs anesthetized with methoxyflurane and nitrous oxide (n = 3). This procedure is also appropriate for use with human plasma; DAS levels were 24.3 +/- 12.8 pmol/ml DA3S and 9.07 +/- 3.9 pmol/ml DA4S (n = 6).

Sample preparation procedure for determination of dopamine sulfate isomers in human urine by high-performance liquid chromatography with dual-electrode electrochemical detection

We developed a procedure utilizing small columns of solid-phase extraction material for sample preparation for the determination of dopamine sulfate (DAS) isomers in human urine. Processed sample is then subjected to high-performance liquid chromatography (HPLC) with dual-series-electrode electrochemical detection. Dopamine 3-O-sulfate (DA-3-S) and dopamine 4-O-sulfate (DA-4-S) were determined using two different HPLC systems. The ratio of the urinary excretion rate of DA-3-S to DA-4-S was relatively constant, but the 24-h excretion rates of total DAS varied widely among individuals. This method should prove useful in future studies concerning the metabolic and physiologic roles of DAS isomers.