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

Clinical Utility of Monoamine Neurotransmitter Metabolite Analysis in Cerebrospinal Fluid

Background: Measurements of monoamine neurotransmitters and their metabolites in plasma and urine are commonly used to aid in the detection and monitoring of neuroblastoma and pheochromocytoma and the evaluation of hypotension or hypertension. Measurements of these neurotransmitters and metabolites can also be helpful in the investigation of disorders that primarily affect the central nervous system, but only when the measurements are made in cerebrospinal fluid (CSF).

Content: I describe CSF profiles of monoamine metabolites in the primary and secondary defects affecting serotonin and catecholamine metabolism. I outline the methods required to analyze these metabolites together with details of specific sample handling requirements, sample stability, and interfering compounds, and I emphasize a need for age-related reference intervals.

Summary: Measured values of monoamine metabolites in CSF provide only a single-time snapshot of the overall turnover of the monoamine neurotransmitters within the brain. Because these measurements reflect the average concentrations accumulated from all brain regions plus the regional changes that occur within the spinal cord, they may miss subtle abnormalities in particular brain regions or changes that occur on a minute-to-minute or diurnal basis. Clearly defined diagnosed disorders are currently limited to those affecting synthetic and catabolic pathways. In many cases, abnormal monoamine metabolite concentrations are found in CSF and an underlying etiology cannot be found. Molecular screening of candidate genes related to steps in the neurotransmission process, including storage in presynaptic nerve vesicles, release, interaction with receptors, and reuptake, might be a fruitful endeavor in these cases.

Detection of neurotransmitters by a light scattering technique based on seed-mediated growth of gold nanoparticles

A simple light scattering detection method for neurotransmitters has been developed, based on the growth of gold nanoparticles. Neurotransmitters (dopamine, L-dopa, noradrenaline and adrenaline) can effectively function as active reducing agents for generating gold nanoparticles, which result in enhanced light scattering signals. The strong light scattering of gold nanoparticles then allows the quantitative detection of the neurotransmitters simply by using a common spectrofluorometer. In particular, Au-nanoparticle seeds were added to facilitate the growth of nanoparticles, which was found to enhance the sensing performance greatly. Using this light scattering technique based on the seed-mediated growth of gold nanoparticles, detection limits of 4.4 × 10(-7) M, 3.5 × 10(-7) M, 4.1 × 10(-7) M, and 7.7 × 10(-7) M were achieved for dopamine, L-dopa, noradrenaline and adrenaline, respectively. The present strategy can be extended to detect other biologically important molecules in a very fast, simple and sensitive way, and may have potential applications in a wide range of fields.

Simultaneous determination of serum concentrations of levodopa, dopamine, 3-O-methyldopa and alpha-methyldopa by HPLC

Levodopa is the medication of choice for Parkinson's disease. The biological complexity of levodopa and of its main derivatives makes their determination important in the clinical field. The aim of this study was to develop an HPLC method for the simultaneous determination of serum concentrations of levodopa, dopamine, 3-O-methyldopa and alpha-methyldopa. We compared UV and fluorimetric detection of native and derivatised compounds. Though less sensitive than other methods, UV detection is important to exclude naturally fluorescent, interfering substances. Fluorimetric detection of derivatised compounds is more sensitive than UV detection. Since 3-O-methyldopa does not react with the derivatising agent 1,2-diphenylethylenediamine, it cannot be detected. For simultaneous determination of the four compounds after pharmacological treatment of patients we therefore advise fluorimetric detection of the native compound.

Analysis of inorganic and small organic ions by CE with amperometric detection

Capillary electrophoresis has become a widely useful analytical technology. Amperometric detection is extensively employed in capillary electrophoresis for its many inherent virtues, such as rapid response, remarkable sensitivity, and low cost of both detectors and instrumentations. Analysis of inorganic and small organic ions by capillary electrophoresis is an important research field. This review focuses on the recent developments of capillary electrophoresis coupled with amperometric detection for analysis of inorganic and small organic ions. Advancements in electrophoresis separation modes, amperometric detection modes, working electrodes, and applications of inorganic ions, amino acids, phenols, and amines are discussed.

Determination of endogenous norepinephrine levels in different chambers of the rat heart by capillary electrophoresis coupled with amperometric detection

Capillary electrophoresis with end-column amperometric detection (CE-EC) was used to determine the regional distribution of norepinephrine (NE) in the hearts of sympathetically innervated (control) and chemically sympathectomized rats. Key features of the method are (i) the sample preparation and clean-up step that involved the application of off-line solid phase extraction (SPE) with a 95% NE recovery and (ii) the use of a diamond microelectrode for detection. NE was quantified in the left and right ventricle, the ventricular septum, and the left and right atrium. The NE concentration in the atria was three to five times higher than in the ventricles and ventricular septum of control rats. Basal NE levels in the left and right ventricle and the ventricular septum were reduced to below the detection limit (0.034 microg/g tissue) in tissues treated with the neurotoxin, 6-hydroxydopamine (6-OHDA), while only a moderate reduction was observed in the left and right atrium. Importantly, the diamond microelectrode provided low and stable background current and low peak-to-peak noise <or=0.65 pA at a detection potential of +0.86 V versus Ag/AgCl. A reproducible electrode response was observed for multiple injections of tissue homogenates with minimal response attenuation due to electrode fouling.

Determination of catecholamines by flow-injection analysis and high-performance liquid chromatography with chemiluminescence detection

A chemiluminescence (CL) detection of catecholamines [norepinephrine (NE), epinephrine (E), dopamine (DA) and L-dopa (LD)] is described for the flow-injection (FI) and high-performance liquid chromatographic (HPLC) determination of these compounds. The detection method is based on the inhibition effect of catecholamines (CAs) on the CL reaction of luminol with iodine in the alkaline medium. The proposed FI method allows the determination of CAs in pharmaceutical preparations for the purpose of drug quality control. The calibration curves show good linearity in the concentration range of: 1.1-20.0 microg l(-1) (NE), 0.5-5.0 microg l(-1) (E), 0.6-9.0 microg l(-1) (DA) and 0.6-10.0 microg l(-1) (LD). The limits of detection (defined as a signal-to-noise ratio of 3) are: 0.34 microg l(-1) (NE), 0.15 microg l(-1) (E) and 0.18 microg l(-1) (DA, LD). The HPLC procedure was successfully applied for the determination of catecholamines (NE, E, DA) in human urine after solid-phase extraction (SPE). In a simple run time CAs can be determined in 20 min. The chromatographic linear ranges are: 5.0-72.0 microg l(-1) (NE), 5.0-48.0 microg l(-1) (E) and 5.0-96.0 microg l(-1) (DA). The limits of detection for three urinary CAs are: 0.71 microg l(-1) (NE), 0.26 microg l(-1) (E) and 0.73 microg l(-1) (DA).