Analysis of plasma catecholamines by liquid chromatography with amperometric detection using a novel SPE ion-exchange procedure

Analysis of Catecholamines and Pterins in Inborn Errors of Monoamine Neurotransmitter Metabolism-From Past to Future

Inborn errors of monoamine neurotransmitter biosynthesis and degradation belong to the rare inborn errors of metabolism. They are caused by monogenic variants in the genes encoding the proteins involved in (1) neurotransmitter biosynthesis (like tyrosine hydroxylase (TH) and aromatic amino acid decarboxylase (AADC)), (2) in tetrahydrobiopterin (BH₄) cofactor biosynthesis (GTP cyclohydrolase 1 (GTPCH), 6-pyruvoyl-tetrahydropterin synthase (PTPS), sepiapterin reductase (SPR)) and recycling (pterin-4a-carbinolamine dehydratase (PCD), dihydropteridine reductase (DHPR)), or (3) in co-chaperones (DNAJC12). Clinically, they present early during childhood with a lack of monoamine neurotransmitters, especially dopamine and its products norepinephrine and epinephrine. Classical symptoms include autonomous dysregulations, hypotonia, movement disorders, and developmental delay. Therapy is predominantly based on supplementation of missing cofactors or neurotransmitter precursors. However, diagnosis is difficult and is predominantly based on quantitative detection of neurotransmitters, cofactors, and precursors in cerebrospinal fluid (CSF), urine, and blood. This review aims at summarizing the diverse analytical tools routinely used for diagnosis to determine quantitatively the amounts of neurotransmitters and cofactors in the different types of samples used to identify patients suffering from these rare diseases.

LC–MS/MS method for quantification of 3,4-dihydroxyphenylglycol, a norepinephrine metabolite in plasma and brain regions

Aim: To evaluate suitability of the LC–MS/MS method to quantify 3,4-dihydroxyphenylglycol (DHPG) that is used as a biomarker for monoamine oxidase (MAO) inhibition. Methods: DHPG was extracted using alumina basic cartridges and quantified on a triple quadrupole mass spectrometer using negative electrospray ionization, without the use of derivatization reagents. Results: Modulation of DHPG levels was observed following administration of selective and nonselective MAO inhibitors and results were in correlation with historical MAO inhibition potential of compounds. Conclusion: The proposed method is sensitive enough to measure plasma DHPG levels and DHPG can be used as a biomarker to assess MAO inhibition potential of new therapeutic agents.

Enzyme-Free Plasmonic Biosensor for Direct Detection of Neurotransmitter Dopamine from Whole Blood

Complex biological fluids without pretreatment, separation, or purification impose stringent limitations on the practical deployment of label-free plasmonic biosensors for advanced assays needed in point of care applications. In this work, we present an enzyme-free plasmonic neurotransmitter dopamine biosensor integrated with a microfluidic plasma separator. This integrated device allows the in-line separation of plasma directly from the bloodstream and channels it to the active detection area, where inorganic cerium oxide nanoparticles function as local selective dopamine binding sites through strong surface redox reaction. A thorough understanding and engineering of the nanoparticles is carried out to maximize its dopamine sensitivity and selectivity. We obtain detection of dopamine at 100 fM concentration in simulated body fluid and 1 nM directly from blood without any prior sample preparation. The detection selectivity is found to be at least five-times higher compared to the common interfering species. This demonstration shows the feasibility of the practical implementation of the proposed plasmonic system in detection of variety of biomarkers directly from the complex biological fluids.

A sensitive, high-throughput LC-MS/MS method for measuring catecholamines in low volume serum

A robust, sensitive, high-throughput method for the detection and quantification of catecholamines in serum, including dopamine, 5-methoxytryptamine, tyramine, phenylethylamine (PEA), epinephrine (EPI), norepinephrine (NE), metanephrine (MN), and normetanephrine (NMN) is described. It is based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) in a positive scheduled multiple reaction monitoring (MRM) mode. Key to the success of the method is the inclusion of an amine derivatization step, using phenylisothiocyanate (PITC), prior to liquid chromatographic separation of the targeted analytes on a C18 reversed-phase column. Mass spectrometric conditions, e.g., characteristic fragmentations and quantification transitions were also optimized to obtain maximum sensitivity and specificity. The limits of detection for all the target analytes are in the low nanomolar range. The recovery rates of spiked serum samples with three different concentration levels, i.e., low, medium, and high, are in the range of 93.2%-113% with satisfactory precision values of less than 10.9%. This method was successfully applied to determine the concentrations of dopamine, 5-methoxytryptamine, tyramine, PEA, EPI, NE, MN, and NMN in multiple human serum samples, with results matching closely those reported in the literature. Comparisons to other reported methods for measuring catecholamines indicates this new approach requires 10-20X less volume, making it ideal for targeted metabolomics studies with volume-limited samples. The method has been adapted to a 96-well plate format and has allowed the quantitative determination of catecholamines in more than 800 serum samples on a single instrument in just nine days.

Preparation of an aminopropyl imidazole-modified silica gel as a sorbent for solid-phase extraction of carboxylic acid compounds and polycyclic aromatic hydrocarbons

In this paper, a kind of aminopropyl imidazole-modified silica sorbent was synthesized and used as a solid-phase extraction (SPE) sorbent for the determination of carboxylic acid compounds and polycyclic aromatic hydrocarbons (PAHs). The resultant aminopropyl imidazole-modified silica sorbent was characterized by Fourier transform infrared spectroscopy (FT-IR) and elemental analysis (EA) to ensure the successful binding of aminopropyl imidazole on the surface of silica gel. Then the aminopropyl imidazole-modified silica sorbent served as a SPE sorbent for the enrichment of carboxylic acid compounds and PAHs. The new sorbent exhibited high extraction efficiency towards the tested compounds and the results show that such a sorbent can offer multiple intermolecular interactions: electrostatic, π-π, and hydrophobic interactions. Several parameters affecting the extraction recovery, such as the pH of sample solution, the pH of eluent, the solubility of eluent, the volume of eluent, and sample loading, were also investigated. Under the optimized conditions, the proposed method was applied to the analysis of four carboxylic acid compounds and four PAHs in environmental water samples. Good linearities were obtained for all the tested compounds with R(2) larger than 0.9903. The limits of detection were found to be in the range of 0.0065-0.5 μg L(-1). The recovery values of spiked river water samples were from 63.2% to 112.3% with relative standard deviations (RSDs) less than 10.1% (n = 4).

Biogenic amines and their metabolites in mouse brain tissue: development, optimization and validation of an analytical HPLC method

A simple and fast HPLC method based on an isocratic, reversed-phased ion-pair with amperometric end-point detection for simultaneous measurement of noradrenergic (MHPG/NA and A), dopaminergic (DOPAC, HVA/DA) and serotonergic (5-HIAA/5-HT) compounds in mouse brain tissue was developed. In order to improve the chromatographic resolution (Rs) with an acceptable total analysis time, experimental designs for multivariate optimization of the experimental conditions were applied. The optimal conditions for the separation of the eight neurotransmitters and metabolites, as well as two internal standards, i.e., DHBA and 5-HMT, were obtained using a mixture of methanol-phosphate-citric buffer (pH 3.2, 50 mM) (9:91, v/v) containing 2 mM OSA as mobile phase at 32°C on a microbore ALF-115 column (150 mm × 1.0 mm, 3 μm particle size) filled with porous C(18) silica stationary phase. In this study, a two-level fractional factorial experimental design (½ 2(K)) was employed to optimize the separation and capacity factor (k') of each molecule, leading to a good separation of all biogenic amines and their metabolites in brain tissue. A simple method for the preparation of different bio-analytical samples in phosphate-citric buffer was also developed. Results show that all molecules of interest were stabilized for at least 24 h in the matrix conditions without any antioxidants. The method was fully validated according to the requirements of SFSTP (Société Française des Sciences et Techniques Pharmaceutiques). The acceptance limits were set at ±15% of the nominal concentration. The method was found accurate over a concentration range of 4-2000 ng/ml for MHPG, 1-450 ng/ml for NA, 1-700 ng/ml for A, 1-300 ng/ml for DOPAC, 1-300 ng/ml for 5-HIAA, 1-700 ng/ml for DA, 4-2800 ng/ml for HVA and 1-350 ng/ml for 5-HT. The assay limits of detection for MHPG, NA, A, DOPAC, 5-HIAA, DA, HVA and 5-HT were 2.6, 2.8, 4.1, 0.7, 0.6, 0.8, 4.2 and 1.4 pg, respectively. It was found that the mean inter- and intra-assay relative standard deviations (RSDs) over the range of standard curve were less than 3%, the absolute and the relative recoveries were around 100%, demonstrating the high precision and accuracy, and reliability of the analytical method described to apply in routine analysis of biogenic amines and their metabolites in brain tissue.

Quantitative chiral analysis of salsolinol in different brain regions of rats genetically predisposed to alcoholism

A method to determine the catecholamine content in putamen (CPU) and midbrain (MB) regions of the brain of alcohol-preferring rats (P) is presented with a focus on the low-level detection of S,R-salsolinol, a metabolite of dopamine and a putative alcoholism marker. The developed strategy allows both quantitative profiling of related catecholamines and the enantiomeric separation and quantification of the S- and R-salsolinol isomers and their ratios. The described LC/MS strategy simplifies the current methodology that typically employs GC-MS by eliminating the need for derivatization. The data also suggest an increase in the non-enzymatic formation of salsolinol as a consequence of ethanol exposure.

Determination of salsolinol and related catecholamines through on-line preconcentration and liquid chromatography/atmospheric pressure photoionization mass spectrometry

A new analytical approach has been developed for simultaneous measurements of endogenous salsolinol and major catecholamines in brain tissue of experimental animals. This procedure involves a combination of on-line phenyl boronate affinity preconcentration and microcolumn liquid chromatography, followed by mass spectrometry equipped with an atmospheric pressure photoionization (APPI) source. Flow conditions of the APPI source were optimized for detection sensitivity while different dopants were evaluated. The on-line preconcentration was found essential for the sensitivity requirements of salsolinol measurements in the brain tissue from alcohol-preferring rats subjected to different levels of alcohol exposure.

Determination of homovanillic acid (HVA) in human plasma by HPLC with coulometric detection and a new SPE procedure

A sensitive high-performance liquid chromatographic method has been developed for the determination of homovanillic acid (HVA), the main metabolite of dopamine, in human plasma. Analyses were carried out on a reversed-phase column (C8, 250 mm x 4.6 mm i.d., 5 microm) using a mobile phase composed of 10% methanol and 90% aqueous citrate buffer, containing octanesulfonic acid and EDTA at pH 4.8. Coulometric detection was used, setting the guard cell at +0.100 V, the first analytical cell at -0.200 V and the second analytical cell at +0.500 V. A careful solid-phase extraction procedure, based on strong anion exchange (SAX) cartridges (100 mg, 1 mL), was implemented for the pre-treatment of plasma samples. Extraction yield was satisfactory, being the mean value 98.0%. The calibration curve was linear over the concentration range of 0.2-25.0 ng mL(-1) of homovanillic acid. The limit of quantitation (LOQ) was 0.2 ng mL(-1) and the limit of detection (LOD) was 0.1 ng mL(-1). The method was successfully applied to plasma samples from former alcohol, cocaine and heroin addicts. Results were satisfactory in terms of precision and accuracy. Hence, the method is suitable for the determination of homovanillic acid in human plasma.

Recent advances in methods for the analysis of catecholamines and their metabolites

Catecholamines, for example epinephrine, norepinephrine, and dopamine, are widely distributed and are important neurotransmitters and hormones in mammalian species. Several methods have been developed for analysis of catecholamines and related compounds. Determination of catecholamines in biological fluids has enabled us to clarify the physiological role played by these amines. Catecholamine levels in plasma and/or urine are also useful for diagnosis of several diseases, for example hypertension, pheochromocytoma, and neuroblastoma. This review covers reports from 2000 to the present of methods for the analysis of catecholamines and their metabolites.

Simultaneous liquid chromatographic analysis of catecholamines and 4-hydroxy-3-methoxyphenylethylene glycol in human plasma

The comparison of two HPLC methods, one with electrochemical detection and the other with coulometric detection, for the simultaneous analysis of catecholamines and 4-hydroxy-3-methoxyphenylethylene glycol (MHPG) in human plasma is presented. The careful pre-treatment of plasma samples is based on an innovative two-step procedure by means of solid-phase extraction (SPE) which uses one single hydrophilic-lipophilic balance cartridge. The extraction yield values found were higher than 85% for epinephrine, norepinephrine and MHPG, and higher than 70% for dopamine. The assays carried out on real plasma samples with the coulometric system gave good results in terms of sensitivity (limits of quantitation: 0.10-0.15 ng ml(-1) for catecholamines, 0.6 ng ml(-1) for MHPG) and selectivity, while interference was sometimes found when using the amperometric system. Precision was also satisfactory, with relative standard deviation values for intermediate precision always lower than 6%. The HPLC method with coulometric detection coupled to a novel SPE procedure is thus suitable for the simultaneous determination of catecholamines and MHPG in plasma of volunteers subjected to experimental stress.