Rapid assay of the monoamine content in small volumes of rat plasma

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.

Fluoxetine increases extracellular levels of 3-methoxy-4-hydroxyphenylglycol in cultured COLO320 DM cells

Fluoxetine (Prozac) is a serotonin reuptake inhibitor. It increases extracellular levels of serotonin and is used in relieving the depressive symptoms of cancer patients. It has been reported that the drug may enhance the growth of certain cancer cells. This study investigates whether fluoxetine enhances the growth of a human colon cancer cell line (COLO320 DM) and if it affects the extracellular levels of serotonin or its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA) and other monoamines and metabolites at two cell densities. The extracellular levels of serotonin, 5-HIAA and other monoamines and metabolites were measured simultaneously by high performance liquid chromatography from cell-culture media after incubation of cells both with and without fluoxetine for 3 days. The viability of COLO320 DM cells was evaluated using 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). At low cell densities (1.25x10(5) cells ml-1), fluoxetine at 1-10 microM significantly increased the extracellular levels of serotonin (p<0.005), 5-HIAA (p<0.005), and 3-methoxy-4-hydroxyphenylglycol (MHPG; p<0.001) as compared to the controls. Fluoxetine at 10-100 microM significantly inhibited the growth of COLO320 DM (p<0.005). At high cell densities (2x10(6) cells ml-1), fluoxetine at 1-10 microM significantly increased the extracellular levels of MHPG (p<0.01), and at 10 microM it significantly increased the extracellular levels of 5-HIAA (p<0.05). Fluoxetine at 100 microM significantly inhibited the growth of the cells (p<0.0001). These results suggest that fluoxetine at 1 microM of effective concentration may increase the extracellular levels MHPG, in addition to serotonin and 5-HIAA levels, yet not inhibit the growth of COLO320 DM.

Simultaneous HPLC of twelve monoamines and metabolites shows neuroblastoma cell line releases HVA and HIAA

Neuroblastoma is a solid tumor occurring usually in children less than 5 years old. It has been difficult to distinguish neuroblastoma from other childhood tumors through morphological diagnosis. Urine homovanillic acid (HVA), which is a metabolite of dopamine, has been proposed as a diagnostic index. Although increased levels of a serotonin metabolite, 5-hydroxyindole-3-acetic acid (HIAA), have also been observed in urine samples of the patients, they were largely attributed to dietary amines. By using an HPLC system with electrochemical detection, which can simultaneously assay 12 monoamines and metabolites, we showed that HVA and HIAA are two of the most prominent monoamine metabolites in the medium after a neuroblastoma cell line (IMR-32) was cultured for 3 days. Moreover, we found that the levels of HVA and HIAA in the media are proportional to the cell densities. These results suggest that the levels of HVA and HIAA in tissue culture media, or in urine from patients whose dietary amines are well controlled, may provide a valuable diagnostic index for neuroblastoma.

Laser-induced fluorescence detection by liquid core waveguiding applied to DNA sequencing by capillary electrophoresis

A new laser-induced fluorescence detector for capillary electrophoresis (CE) is described. The detector is based on transverse illumination and collection of the emitted fluorescent light via total internal reflection along the separation capillary. The capillary is coated with a low refractive index fluoropolymer and serves as a liquid core waveguide (LCW). The emitted light is detected end-on with a CCD camera at the capillary exit. The observed detection limit for fluorescein is 2.7 pM (550 ymol) in the continuous-flow mode and 62 fM in the CE mode. The detector is applied to DNA sequencing. One-color G sequencing is performed with single-base resolution and signal-to-noise ratio approximately 250 for peaks around 500 bases. The signal-to-noise ratio is approximately 50 for peaks around 950 bases. Full four-color DNA sequencing is also demonstrated. The high sensitivity of the detector is suggested to partly be due to the efficient rejection of scattered laser light in the LCW. The concept should be highly suitable for capillary array detection.

Determination of norepinephrine in small volume plasma samples by stable-isotope dilution gas chromatography-tandem mass spectrometry with negative ion chemical ionization

A stable-isotope based gas chromatography-tandem mass spectrometry-negative ion chemical ionization method was developed for the determination of norepinephrine (NE) levels in small volumes (25-100 microl) of plasma. NE was stabilized in plasma by the addition of semicarbazide and spiked with deuterium-labeled norepinephrine internal standard. The analytes were isolated from the plasma by solid-phase extraction using phenylboronic acid columns and derivatized using pentafluoropropionic anhydride. The derivatized analytes were chromatographed on a capillary column and detected by tandem mass spectrometry with negative ion chemical ionization. Unparalleled sensitivity and selectivity were obtained using this detection scheme, allowing the unambiguous analysis of trace levels of NE in small-volume plasma samples. Linear standard curves were obtained for NE over a mass range from 1 to 200 pg per sample. The method had a limit of quantitation of 10 pg NE/ml plasma when using a 100-microl sample aliquot (1 pg/sample). Accuracy for the analysis of plasma samples spiked with 10 to 200 pg NE/ml typically ranged from 100+/-10%, with RSD values of less than 10%. The methodology was applied to determine the effect of clonidine on plasma NE levels in conscious spontaneously hypertensive rats. Administration of clonidine (30 microg/kg) produced an approximately 80% reduction in plasma NE accompanied by a 30% reduction in heart and mean arterial pressure that persisted >90 min after drug administration. The ability to take multiple samples from individual rats allowed the time course for the effect of clonidine to be mapped out using only one group of animals.

Characterization of the rat adrenal medulla cultured in vitro

A wide variety of experimental animal models have been used to investigate the mechanisms of synthesis, storage, and release of catecholamines. Whereas in vivo experimental models are situated at one end of the spectrum, cell culture models are situated at the other end. In the present study, we have characterized various aspects of the rat adrenal medulla cultured in vitro as a whole tissue, aiming to establish a new experimental model in between in vivo animal models and cell culture models. We adapted a bottle rotator system commonly used for culturing rodent whole embryos. Changes in histology, activities and mRNA levels of catecholamine-synthesizing enzymes, and concentrations of catecholamines in the adrenal medulla were studied. In addition, the effects of cholinergic stimulation on catecholamine release from the adrenal medulla were examined. Overall the results indicate that various aspects of the adrenal medulla become stable after 4 d of culture and the adrenal medulla at this stage releases catecholamines in response to cholinergic stimulation. The whole adrenal medulla culture system may be a useful tool for investigating catecholamine-related functions dependent on intercellular reactions or communications.

Monitoring of blood catecholamines by microdialysis and microbore LC with a dual amperometric detector

The accuracy of in vivo microdialysis for monitoring blood catecholamines and their metabolites in Lan-Yu mini-pigs was evaluated. To prevent blood clots and irritation, a microdialysis probe was secured in a Y-shaped tube. The tube was connected to an arterio-venous shunt, in a mini-pig, for in vivo experiments. Perfusates were injected onto a microbore LC equipped with a dual electrochemical detector (the upstream electrode was set at an oxidizing potential and the downstream electrode was set at a reducing potential. The typical large offscale peak or interfering peaks on the anodic chromatograms were mostly eliminated on the cathodic chromatograms, thereby providing reliable measurements of early eluters. Early eluates, such as norepinephrine and epinephrine, with reversible redox behaviour could be detected at the downstream reducing electrode. A comparison of the present method and a conventional blood-drawing method showed good correlation (r = 0.775-0.983 for all analytes).

New dual electrochemical detector for microbore liquid chromatography. Determination of dopamine and serotonin in rat striatum dialysates

A new type of liquid chromatographic (LC) dual thin-layer amperometric detector for the simultaneous measurement of trace levels of dopamine and serotonin in microdialysates is described. The concentrations of these analytes in rat dialysates are usually in the sub-nanomolar concentration range (typically, 0.10-5.00 pg in 5-microl dialysates). With this dual electrode, a glass-lined microbore column provides excellent sensitivity, selectivity, and separation. In addition, a three- to five-fold improvement in anodic current or cathodic responses over conventional dual electrodes in microbore LC can be achieved. Due to the irreversible electrochemical properties of some interference peaks, this dual electrode provides reliable measurement of dopamine based on the cathodic signal. The detection limit (signal-to-noise ratio = 3) of this assay is 0.02 pg per injection for dopamine or serotonin. This new dual electrode allows the simultaneous measurements of basal dopamine and serotonin in rat striatum dialysates without the use of re-uptake inhibitors in perfusion medium.

High-performance liquid chromatographic analysis with electrochemical detection of biogenic amines using microbore columns

High-performance liquid chromatography with electrochemical detection (HPLC-ED) is a popular method for measuring biogenic amines, owing to its simplicity, versatility, sensitivity, and specificity. Recent developments in microbore column HPLC-ED have been facilitated by miniaturization of solvent delivery, column packing, sample injection and micro-flow cell construction. The aim of this paper is to present an overview of recent developments in microbore column HPLC-ED, in terms of advantages and limitations. This paper covers the recent advancements and important factors of HPLC-ED analysis of biogenic amines using microbore columns. Particular emphasis is placed on applying this technique to microdialysis, for which great sensitivity is required. Its potential in future biomedical applications is also discussed.