Determination of catecholamines by automated precolumn derivatization and reversed-phase column liquid chromatography with fluorescence detection

Simultaneous determination of catecholamines and their metabolites related to Alzheimer's disease in human urine

A simple and specific high-performance liquid chromatography method coupled with fluorescence detection (HPLC-FL) has been developed for the simultaneous determination of L-3,4-dihydroxyphenylalanine, norepinephrine, dopamine, epinephrine and 3,4-dihydroxyphenylacetic acid in human urine. The samples were derivatized by 1,2-diphenylethylenediamine with isoprenaline as internal standard. The factors affecting the fluorescence yield were investigated, including the reaction and separation conditions. The catecholamine derivatives were separated on a Kromasil C(18) column with methanol and sodium acetate buffer as mobile phase. The limits of detection for all catecholamines ranged from 0.2 to 1.1 ng/mL. The linear ranges were from 2.5 to 200 ng/mL except 3,4-dihydroxyphenylacetic acid from 5 to 200 ng/mL. The intra- and interday RSDs for all catecholamines were 1.0-8.0 and 2.1-14%, respectively. The method was successfully applied to determine the catecholamines in human urine from 14 Alzheimer's disease patients and 14 healthy volunteers. It was concluded that the mean levels of catecholamines in urine of Alzheimer's disease patients were all lower than those in healthy volunteers. The cluster analysis and independent samples T-test were used to distinguish the Alzheimer's disease patients and healthy volunteers.

Simultaneous determination of biogenic monoamines in rat brain dialysates using capillary high-performance liquid chromatography with photoluminescence following electron transfer

Simultaneous determination of biogenic monoamines such as dopamine, serotonin, and 3-methoxytyramine in brain is important in understanding neurotransmitter activity. This study presents a sensitive determination of biogenic monoamines in rat brain striatum microdialysates using capillary high-performance liquid chromatography with the photoluminescence following electron-transfer detection technique. Separation conditions were optimized by changing the concentration of an ion-interaction agent and the percentage of an organic modifier. The high concentration of ion-interaction agent enabled the amines as a class to be separated from interfering acids, but also made the separation very long. To shorten the separation time, 10% (v/v) acetonitrile was used as the organic modifier. Eight chromatographic runs during a 3-h period were analyzed in terms of retention times, peak heights, and peak widths. Chromatograms are very reproducible, with less than 1% changes in peak height over 3 h. Typical concentration detection limits at the optimum separation conditions were less than 100 pM for metabolic acids and approximately 200 pM for monoamines. The injection volume of the sample was 500 nL. Thus, the mass detection limits were less than 50 amol for metabolic acids and approximately 100 amol for monoamines. Typical separation time was less than 10 min. To validate the technique, the separation method was applied to the observation of drug-induced changes of monoamine concentrations in rat brain microdialysis samples. Local perfusion of tetrodotoxin, a sodium channel blocker, into the striatum of an anesthetized rat decreased dopamine, 3-methoxytyramine, and serotonin concentrations in dialysates. Successive monitoring of striatal dialysates at a temporal resolution of 7.7 min showed that the injection of nomifensine transiently increased dopamine and 3-methoxytyramine concentrations in rat brain dialysate.

Derivatization chemistries for determination of serotonin, norepinephrine and dopamine in brain microdialysis samples by liquid chromatography with fluorescence detection

The present paper provides an overview on currently developed derivatization chemistries and techniques for determination of monoamine neurotransmitters serotonin (5-HT), norepinephrine (NE) and dopamine (DA) in microdialysis samples by microbore liquid chromatography with fluorescence detection. In mild alkaline conditions, 5-hydroxyindoles and catecholamines react with benzylamine (BA), forming highly fluorescent 2-phenyl-4,5-pyrrolobenzoxazoles and 2-phenyl(4,5-dihydropyrrolo) [2,3-f]benzoxazoles, respectively. However, for derivatization of DA a higher fluorescence intensity was achieved for reaction with 1,2-diphenylethylenediamine (DPE) rather than with BA, therefore for simultaneous determination of 5-HT, NE and DA in brain microdialysates, a two-step derivatization with BA followed by DPE was developed. The detection limits for 5-HT, NE and DA were 0.2, 0.08 and 0.13 fmol, respectively, in an injection volume of 20 microL, which corresponds to concentrations of 30, 12 and 19.5 pm, respectively in standard solution prior to derivatization. The experimental data presented demonstrate the ability of the technique to simultaneously monitor neuronally releasable pools of monoamine neurotransmitters in the rat and mouse brains at basal conditions and following pharmacological treatments or physiological stimuli. These techniques play an important role in drug discovery and clinical investigation of psychiatric and neurological diseases such as depression, schizophrenia and Parkinson's disease.

High-sensitive liquid chromatographic method for determination of neuronal release of serotonin, noradrenaline and dopamine monitored by microdialysis in the rat prefrontal cortex

A high-sensitive liquid chromatographic method based on precolumn derivatization and fluorescence detection allowing simultaneous determination of serotonin (5-HT), noradrenaline (NA) and dopamine (DA) in brain microdialysis samples is described. 5-HT, NA and DA were derivatized with benzylamine and 1,2-diphenylethylenediamine in the presence of potassium hexacyanoferrate(III) and glycine, which yielded to highly fluorescent and stable benzoxazoles. The derivatized samples were separated on a microbore column (150 mm x 1.0mm i.d., packed with C18 silica, 5 microm) within 60 min. The mobile phase consisted of acetonitrile-Briton-Robinson buffer (pH 7.2) (32:68, v/v) containing 5 mM Na2EDTA and 5 mM octanesulfonic acid sodium salt. The detection limits (signal-to-noise ratio of 3) for 5-HT, NA and DA were 76, 42 and 95 amol/10 microl injected on-column, respectively. Microdialysis samples were collected at 10-min intervals from the probes implanted in the prefrontal cortex of awake rats. The basal levels of 5-HT, NA and DA were 7.3 +/- 0.7, 5.3 +/- 0.31 and 8.1 +/- 0.47 fmol/5 microl (mean +/- S.E.M., n = 5). Following 90-min perfusion with tetrodotoxin (1 microM) or calcium-free Ringer solution, the DA and NA levels were reduced to about 15 and 20%, respectively and the 5-HT levels to 45 and 60% of the basal levels, respectively. Reserpine, 12h after a dose of 5mg/kg i.p., reduced the extracellular 5-HT, NA and DA concentrations to about 34, 39 and 32% of the basal levels, respectively. In conclusion, the preset microdialysis/analytical method enables simultaneous monitoring of basal and pharmacologically reduced neuronal release of 5-HT, NA and DA in the rat brain.

Determination of serotonin, noradrenaline, dopamine and their metabolites in rat brain extracts and microdialysis samples by column liquid chromatography with fluorescence detection following derivatization with benzylamine and 1,2-diphenylethylenediamine

A highly selective and sensitive column liquid chromatographic method for fluorescence determination of serotonin (5-HT), dopamine (DA), noradrenaline (NA) and their related metabolites 5-hydroxyindole-3-acetic acid (5-HIAA) and 3,4-dihydroxyphenylacetic acid (DOPAC) following derivatization with benzylamine and 1,2-diphenylethylenediamine (DPE) is described. The monoamines and the metabolites (20 microl samples) were derivatized in a two-step reaction, initiated with 20 microl of 0.3M benzylamine in 0.3M 3-cyclohexylaminopropanesulfonic acid (CAPS) buffer (pH 10.0), (for 5-HT, 5-HIAA, 2 min, 24 degrees C) and followed by 20 microl of 0.1M DPE in 0.3M glycine buffer (pH 10.0), (for DA, NA, DOPAC, 20 min, 50 degrees C). Both reagents contained 0.02 M potassium hexacyanoferrate(III) and 50% (v/v) methanol. The resulting highly fluorescent and stable benzoxazole derivatives were isocratically separated on a reversed-phase column (150 mm x 1.5 mm i.d., packed with C18 silica, 5 microm) within 45 min. Using fluorescence detection at ex. and em. wavelengths of 345 and 480 nm, respectively, the detection limit (signal-to-noise ratio of 3) for 5-HT, DA, NA, 5-HIAA, L-DOPA and DOPAC ranged between 0.08 and 5.65 fmol per 20-microl injection (12-847.5 pM in standard solution). The concentrations of monoamines (expressed in microg/g wet weight, mean +/- S.E.M., n=5) in tissue extracts from the rat striatum were: 0.45+/-0.05 (5-HT), 4.27+/-0.08 (DA), 0.27+/-0.04 (NA), 0.55+/-0.06 (5-HIAA), 1.26+/-0.16 (L-DOPA) and 1.62+/-0.11 (DOPAC). Microdialysis samples were collected in 20 min intervals from the probes implanted in the striatum of awake rats. The basal monoamine levels (in fmol/20 microl, mean +/- S.E.M., n=5) in the dialysates were: 4.0+/-0.7 (5-HT), 78.4+/-9.1 (DA), 6.4+/-0.8 (NA), 785.5+/-64.5 (5-HIAA) and 5504.5+/-136.5 (DOPAC). It is concluded that the new fluorescence derivatization protocol provides an excellent means for simultaneous determination of all three monoamines both in the complex samples (e.g. brain homogenates) and also at trace levels, such as those found in the microdialysis samples.

N-hydroxysuccinimidyl fluorescein-O-acetate as a fluorescent derivatizing reagent for catecholamines in liquid chromatography

A new amine-reactive derivatizing reagent, N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA), was developed for catecholamine (CA) analysis in liquid chromatography. The reactivity of this reagent with the CAs norepinephrine (NE), epinephrine (E), and dopamine (DA) was investigated in detail. In aqueous methanol containing 32 mmol/L pH 9.0 H3BO3-Na2B4O7 buffer, SIFA reacted with NE, E, and DA under mild conditions. The derivatives were separated in 20 min on a C18 column with a mobile phase of methanol/water (38:62, v/v) containing 10 mmol/L pH 5.0 H3cit-Na2HPO4 buffer. At lambda(ex)/lambda(em) = 490/516 nm, the detection limits were 3.2, 12, and 56 fmol, respectively, with a signal-to-noise ratio of 3, which were comparable to those using 1,2-diphenylethylenediamine as the derivatizing reagent for CA analysis. Amino acids, aliphatic amines, and alcohols had no obvious interference with the determination. The proposed method has been applied to the determination of CAs in human urine, with recoveries of 95.3-103.9%.

Sensitive and specific method for the simultaneous determination of natural and synthetic catecholamines and 3,4-dihydroxyphenylglycol in microdialysis samples

The relatively new technique of microdialysis provides new possibilities for investigating in vivo the functioning of the sympathetic nervous system. The small sample volumes obtained, however, are a great challenge for analytical chemists. We report here a HPLC method for measuring in one run both natural and synthetic catecholamines [dopamine, (nor)epinephrine, alpha-methylnorepinephrine, isoproterenol and epinine] and the intraneuronal metabolite 3,4-dihydroxyphenylglycol in small microdialysis samples after derivatization with the fluorogenic agent 1,2-diphenylethylenediamine. No prior clean-up step is necessary. N-Ethylmaleimide is necessary for preventing an inhibitory action on derivatization occurring in in vivo microdialysis samples. The method can handle large numbers of samples, is sensitive (on-column detection limits 30 to 200 fg) and reproducible (RSD 1 to 7%). Recovery characteristics of the commercial microdialysis probe used (CMA/20) were extensively investigated both in vitro and in vivo at various perfusion rates; for practical purposes a rate of 2 microl/min and sampling at 10-min intervals was found to be workable and to give good and reproducible recoveries (50 to 70%).

The assay of the catecholamine content of small volumes of human plasma

Plasma catecholamines are routinely measured using high-performance liquid chromatography (HPLC) with electrochemical detection. Most of the present assays require sample volumes of at least 500 microL and are complex and labour-intensive procedures, or require large capital investment to reduce the sample size. This paper describes a liquid/liquid plasma catecholamine extraction procedure, HPLC separation and electrochemical detection method which is simple, sensitive and reproducible. The resting catecholamine concentration of 50 microL adult human plasma can be assayed using standard electrochemical detection. The limits of detection were 0.1 fmol injected onto the column for each catecholamine. This method allows the routine assay of plasma catecholamine concentrations within the normal adult ranges in both 500 and 50 microL samples. The within assay coefficient of variation (CV) for noradrenaline (NA) was 1.2% in 500 microL plasma and 1.9% for 50 microL plasma, corresponding values for adrenaline (A) were 8.5 and 6.6%. The between assay CVs were 3.9 and 7.8% for NA, and 9.9 and 5.7% for A.

Study of salivary catecholamines using fully automated column-switching high-performance liquid chromatography

Cortisol and catecholamines are major physiological markers of human stress. In order to establish a fully automated assay system for both cortisol and catecholamines in saliva, which can be sampled without imposing stress, the previously developed system for salivary cortisol [Okumura et al., J. Chromatogr. B, 670 (1995) 11] was modified. The practical sensitivity was around 0.1 pmol ml(-1) for norepinephrine and epinephrine and 0.5 pmol ml(-1) for dopamine. The established assay procedure provided R.S.D. values of 2 approximately 3% and recoveries of 96 approximately 104% at 0.5 pmol ml(-1). Measurement of salivary catecholamines in more than 300 samples taken from about 50 healthy volunteers indicated that the normal values of norepinephrine and dopamine were very low, about 0.1 pmol ml(-1) each. In contrast to cortisol, salivary catecholamine levels did not parallel those in plasma. Nevertheless, since levels of salivary catecholamines may reflect the sympathetic nerve activity in the salivary gland, they were assayed in volunteers making a scientific presentation before a large audience. Four out of eleven volunteers reported strong feelings of fear or anxiety, and their salivary catecholamine levels were about ten times higher than normal.

In vivo monitoring of extracellular noradrenaline and glutamate from rat brain cortex with 2-min microdialysis sampling using capillary electrophoresis with laser-induced fluorescence detection

The measurement of neurotransmitters by capillary electrophoresis (CE) has emerged as a reliable and sensitive method for microdialysis sample analysis. This paper describes a method which employs laser-induced fluorescence detection (LIFD) of catecholamines and excitatory amino acid derivatives formed after reaction with naphthalene-2,3-dicarboxaldehyde. On-line derivatization of very small volumes of microdialysis samples (500 nl) is developed before two off-line analyses (total run time of less than 10 min) are performed to detect derivatives of catecholamines and excitatory amino acids formed in each sample. High microdialysis temporal resolution is reached (2-min fractions) for the simultaneous monitoring of noradrenaline (NA) and glutamate concentrations from rat brain cortex microdialysates. The system performance is evaluated and pharmacological characterization of the determination of NA in cortical dialysates by CE-LIFD is reported.

Enhanced temporal resolution for the microdialysis monitoring of catecholamines and excitatory amino acids using capillary electrophoresis with laser-induced fluorescence detection. Analytical developments and in vitro validations

This paper reports the development of a method based on capillary electrophoresis with laser-induced fluorescence detection for the simultaneous determination of catecholamines and excitatory amino acids on submicroliter microdialysis samples, with short analysis times (3 min or less), high sensitivity (nanomolar range, i.e., attomoles detected) and high separation efficiency (up to 1.10(6) theoretical plates). A continuous flow derivatization of small volumes of microdialysate (500 nl) using naphthalene-2,3-dicarboxaldehyde as derivatizing reagent is described. Thereafter, two subsequent off-line analyses are performed on each of the 30-s dialysates to determine catecholamines and amino acids. The performances of the present method are demonstrated in vitro by monitoring rapid fluctuations in the concentration of catecholamines and amino acids in the external microdialysis medium.

Parasympathetic inhibition of pineal indole metabolism by prejunctional modulation of noradrenaline release

The role of the parasympathetic nervous system in rat pineal indole metabolism was investigated by transpineal in vivo microdialysis. On-line coupling to a high performance liquid chromatography system with fluorescence detection (HPLC-FD) allowed simultaneous analysis of three major indolic compounds from the pineal, i.e. serotonin, N-acetylserotonin and melatonin. Infusion of the muscarinic receptor agonists, carbachol and oxotremorine, during the dark period resulted in a marked decrease of melatonin release. This effect was suggested to be mediated by a decrease in N-acetyltransferase activity, since a similar decrease was seen in N-acetylserotonin release, while serotonin levels increased simultaneously. Nicotine did show a very slight effect on the three indoles under these circumstances. Neostigmine failed to influence pineal indole metabolism, indicating that the endogenous tonus of acetylcholine release is either absent or extremely low in the middle of the dark period. The involvement of sympathetic innervation in the muscarinic effects was investigated by measurement of noradrenaline release from the pineal by sensitive off-line HPLC-FD analysis of noradrenaline in the dialysates. Carbachol markedly decreased the noradrenaline input during the infusion. Noradrenaline release returned to baseline values immediately after infusion with carbachol. These data suggest that the in vivo inhibitory effect of muscarinic receptor agonists on pineal melatonin production is mediated by presynaptic muscarinic receptors, located on the sympathetic nerve endings. This prejunctional inhibition of noradrenaline release causes a reduced induction of N-acetyltransferase activity, resulting in decreased melatonin release.