Unequivocal synthesis and characterisation of dopamine 3- and 4-O-sulphates

Radiation metabolomics. 1. Identification of minimally invasive urine biomarkers for gamma-radiation exposure in mice

Gamma-radiation exposure has both short- and long-term adverse health effects. The threat of modern terrorism places human populations at risk for radiological exposures, yet current medical countermeasures to radiation exposure are limited. Here we describe metabolomics for gamma-radiation biodosimetry in a mouse model. Mice were gamma-irradiated at doses of 0, 3 and 8 Gy (2.57 Gy/min), and urine samples collected over the first 24 h after exposure were analyzed by ultra-performance liquid chromatography-time-of-flight mass spectrometry (UPLC-TOFMS). Multivariate data were analyzed by orthogonal partial least squares (OPLS). Both 3- and 8-Gy exposures yielded distinct urine metabolomic phenotypes. The top 22 ions for 3 and 8 Gy were analyzed further, including tandem mass spectrometric comparison with authentic standards, revealing that N-hexanoylglycine and beta-thymidine are urinary biomarkers of exposure to 3 and 8 Gy, 3-hydroxy-2-methylbenzoic acid 3-O-sulfate is elevated in urine of mice exposed to 3 but not 8 Gy, and taurine is elevated after 8 but not 3 Gy. Gene Expression Dynamics Inspector (GEDI) self-organizing maps showed clear dose-response relationships for subsets of the urine metabolome. This approach is useful for identifying mice exposed to gamma radiation and for developing metabolomic strategies for noninvasive radiation biodosimetry in humans.

Syntheses of the sulfoconjugated isomers of norepinephrine and dopamine, controlled by HPLC with ultraviolet detection

The physiological significance of sulfoconjugated catecholamines and their involvement in clinical disorders, e.g. hypertension and Parkinsonism, is poorly investigated. For this reason, the sulfoconjugated isomers of dopamine as well as of norepinephrine were synthesized by modified methods. All isomers and their intermediates could be detected by a reversed-phase high-performance liquid chromatography with ultraviolet detection (HPLC-UV) with short retention times and a good reproducibility. Ion-exchange chromatography with an extended column length improved the separation of the reaction products, and the immediate control by HPLC-UV enabled precise cutting of the fractions. The selection of the fractions with the optimum ratios of product/by-product resulted in improved yields and highest purity. All by-products, e.g. dopamine sulfonic acids, were less than 0.04%, as detected by HPLC-UV and, in addition, the contamination by free catecholamines was only 41 x 10(-4)-87 x 10(-4)%, as measured by HPLC with electrochemical detection (HPLC-ED). The purity was further demonstrated in two highly sensitive biological assays: cAMP production in human mononuclear leukocytes and aggregation of human platelets. The sulfoconjugated catecholamines were characterized by melting point, thin-layer chromatography, infrared spectrum, HPLC-UV, elemental analysis, and unequivocally identified by 1H-NMR.

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.

A review of the methods of chemical synthesis of sulphate and glucuronide conjugates

1. Methods for the synthesis of drug conjugates with sulphuric acid have been reviewed. 2. Some analytical methods are presented for the analysis of sulphate conjugates. 3. The synthesis of several types of N, O and C beta-D-glucuronides is reviewed. Different beta-coupling reactions of protected glucuronides are presented. 4. Application of n.m.r. and mass spectrometry to the analysis of beta-D-glucuronides is discussed.

Analytical techniques for the determination of phenolic amine neurotransmitter conjugates

This paper reviews methods developed in the author's laboratory for the measurement of the two sulfate conjugates of dopamine in biological material. The methods are sensitive enough for most applications relating to dopamine sulfate. Some are applicable to measurement of sulfate conjugates of other phenolic amines.

Factors influencing the recovery of dopamine sulfate in the assay of phenol sulfotransferase

Phenol sulfotransferase activity is often measured by incubating dopamine with a source of the enzyme and the sulfate donor 35S-3'-phosphoadensine-5'-phosphosulfate and then separating the product, 35S-dopamine sulfate, from the substrates using precipitation with barium hydroxide and zinc sulfate. Using dopamine sulfate standards and high performance liquid chromatography with dual-electrode electrochemical detection, we investigated the effects of several parameters on product recovery obtained with this procedure. Amounts of precipitants needed to produce maximal sample-to-blank ratios were determined using crude enzyme preparations from rat brain and human platelets incubated under conditions generating approximately 3 nM dopamine sulfate. Under these conditions, recovery of 3H-DAS standards was 70-80%. Increasing either the concentration of dopamine sulfate or the amounts of precipitants used resulted in concentration-dependent decreases in dopamine sulfate recovery. These data indicate that the recovery of product in this assay may vary with assay conditions, and should be carefully monitored and optimized. Caution should be exercised when using substrates other than dopamine in this assay procedure, since similar factors might also contribute to variable recovery of other products.

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).

Dopamine sulfate formation and phenol sulfotransferase activity in dog and human platelets

High performance liquid chromatography with radioactive flow detection was used to examine the accumulation and sulfoconjugation of dopamine by human and dog platelets. Platelets from both species accumulated similar amounts of dopamine from the incubation medium, but only human platelets were found to convert 3H-dopamine to 3-H-dopamine sulfate. This difference between the two species was associated with a relative absence of phenol sulfotransferase activity in dog platelets as compared to human platelets. Dog platelets did not appear to contain an inhibitor of phenol sulfotransferase activity. Despite the apparent difference in the ability of platelets to form dopamine sulfate, conc concentrations of dopamine-3-O-sulfate and dopamine-4-O-sulfate were similar in dog and human plasma. These data suggest that platelets may represent a potential source of at least some of the dopamine sulfate found in human plasma, but not in dog plasma.

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

A high-performance liquid chromatographic (HPLC) method is reported for the determination of dopamine-3- and -4-O-sulphate isomers in human plasma and urine using an anion exchanger coupled with post-column hydrolysis and fluorimetric detection. Samples of plasma or urine are partially purified on Dowex 1 and Dowex 50 columns and separated using HPLC. These compounds are then hydrolysed and determined automatically by the p-aminobenzoic acid method in a continuous-flow reaction system. As the p-aminobenzoic acid method is very specific for dopamine, it is also possible to determine the isomers by injecting 5-20 microliter of urine or 100-200 microliter of deproteinized plasma directly into the HPLC system without clean-up. The detection limit of the method for both isomers is 0.3 pmol. In normal subjects, the plasma levels of dopamine-3- and -4-O-sulphate are 26.5 (S.D. 11.1) and 2.68 (S.D. 0.34) pmol/ml, and their urinary excretion rates are 1.73 (S.D. 0.56) and 0.27 (S.D. 0.04) nmol/min, respectively. Thus the two isomers are present in both plasma and urine and their urinary excretions reflect directly their plasma levels.