Improved measurement of urinary catecholamines by liquid-liquid extraction, derivatization and high-performance liquid chromatography with fluorimetric detection

Rapid determination of catecholamines in urine samples by nonaqueous microchip electrophoresis with LIF detection

A method was developed for the rapid separation of catecholamines by nonaqueous microchip electrophoresis (NAMCE) with LIF detection, A homemade pump-free negative pressure sampling device was used for rapid bias-free sampling in NAMCE, the injection time was 0.5 s and the electrophoresis separation conditions were optimized. Under the optimized conditions, the samples were separated completely in <1 min. The average migration times of the epinephrine (E), dopamine (DA), and norepinephrine (NE) were 34.26, 43.81, and 50.07 s, with an RSD of 1.05, 1.26, and 0.89% (n = 7), respectively. The linearity of the method ranged from 0.0125 to 2.0 mg/L for E and 0.025~4.0 mg/L for DA and NE, with correlation coefficients ranging between 0.9978 and 0.9986. The detection limits of E, DA, and NE were 2.5, 5.0, and 5.0 μg/L, respectively. The recoveries of E, DA, and NE in spiked urine samples were between 86 and 103%, with RSDs of 4.5~6.8% (n = 5). The proposed NAMCE with LIF detection combined with a pump-free negative pressure sampling device is a simple, inexpensive, energy efficient, miniaturized system that can be successfully applied for the determination of catecholamines in urine samples.

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.

Determination of dopamine and serotonin in human urine samples utilizing microextraction online with liquid chromatography/electrospray tandem mass spectrometry

A specific LC-MS-MS method for the determination of dopamine and serotonin (5-hydroxytryptamine; 5HT) in human urine is described. The analytes were extracted from urine and preconcentrated by microextraction in a packed syringe (MEPS). The new method is very promising, very easy to use, fully automated, of low cost, and rapid in comparison to previously used methods. The method was validated and the standard curves were evaluated by means of quadratic regression and weighted by inverse of the concentration: 1/x for the calibration range 50-4000 microg/L. The MEPS applied polymer (silica-C8) could be used more than 300 times. The extraction recovery was about 50%. The results showed close correlation coefficients (r2 > 0.999) for all analytes in the calibration range studied. The accuracy of MEPS-LC-MS-MS was 100-101% for dopamine and 99-100% for 5HT. The interday precision (n = 3 days), expressed as the RSD%, was 6.0-7.7% for dopamine and 6.1-11% for 5HT. MEPS reduced the handling time by 12 times compared to a published method.

Analysis of Catecholamines in Urine by Positive-Ion Electrospray Tandem Mass Spectrometry

Background: Determination of urinary catecholamines (CATs) is considered important for clinical diagnosis of pheochromocytoma, paraganglioma, and neuroblastoma. The major disadvantages of existing tests include relatively long instrumental analysis time and potential interference from drugs and drug metabolites that are structurally similar to CATs.

Methods: CATs were extracted from a 300-μL aliquot of urine by a two-step liquid-liquid extraction method specific for compounds containing a catechol group. Chromatographic separation did not require the use of ion-pairing reagents, which typically hinder MS detection but are frequently used in HPLC analysis of CATs. Instrumental analysis was performed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in the multiple-reaction monitoring mode. Stable-isotope-labeled CATs were used as internal standards.

Results: Epinephrine (E), norepinephrine (NE), and dopamine (D) were measured within 3.5 min instrumental run time. Quantification limits were 2.5 μg/L for E and D and 10 μg/L for NE. The total imprecision (CV) was ≤9.6%; extraction recoveries were 71% ± 12%.

Conclusions: HPLC with ESI-MS/MS in combination with sample preparation specific to catechol group-containing compounds allows rapid testing for disorders associated with increased CAT concentrations. The method is free of interferences from drugs and drug metabolites, which commonly interfere with HPLC methods.

High-performance liquid chromatographic assay for catecholamines and metanephrines using fluorimetric detection with pre-column 9-fluorenylmethyloxycarbonyl chloride derivatization

A convenient HPLC-fluorescent assay of norepinephrine (NE), epinephrine (E), dopamine (DA) and their 3-O-methylated metabolites, normetanephrine (NM) and metanephrine (MN) was developed. These analytes were coupled to 9-fluorenylmethyloxycarbonyl chloride (FMOC-Cl) before assays. Results showed that using a linear gradient elution, peaks of FMOC-NE, FMOC-E, FMOC-DA, FMOC-NM, FMOC-MN and FMOC-DHBA (3,4-dihydroxybenzylamine, internal standard) were simultaneously resolved within 40 min. Optimization of the chromatographic and derivatization conditions, and validation of the assay were further discussed in the paper. The structures of these derivatives were confirmed by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The molecular ions [M+H]- of FMOC-NE, FMOC-E, FMOC-DA, FMOC-NM and FMOC-MN were m/z 836, 850, 820, 628 and 642, respectively. Based on these findings, the FMOC-derivatives of metanephrines and catecholamines were confirmed to be bi-substituted and tri-substituted respectively at the amino and catechol functional groups. Finally, the assay was successfully applied to the measurement of urinary E, DA, NM and MN after direct derivatization and simple cleaning.

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%.

Effect of salt on insulin sensitivity differs according to gender and degree of salt sensitivity

The aim of the present study was to investigate the effect of salt intake on insulin sensitivity and the relation between salt sensitivity and insulin sensitivity in genetically hypertension-prone individuals. Twenty-eight healthy subjects (13 men and 15 women) with a family history of hypertension were examined at baseline, after 1 week of salt restriction (10 mmol/d), and after 1 week of salt loading (240 mmol/d). Insulin sensitivity was measured with the hyperinsulinemic euglycemic clamp after the low- and high-salt diets. Salt sensitivity was defined as the difference in mean arterial blood pressure between the high-salt and the low-salt diets. There was no significant relationship between insulin sensitivity and salt sensitivity after either of the 2 diets. In the men, salt sensitivity was inversely related to plasma renin activity (r=-0.61, P=0.03) and plasma aldosterone (r=-0.74, P=0.004), whereas salt sensitivity in women was directly correlated with the salt-induced increase in body weight (r=0.68, P=0.005). In men, the high-salt diet induced a change in glucose disposal that was strongly correlated with the degree of salt sensitivity (r=0.83, P=0. 0004), plasma renin activity (r=-0.82, P=0.0006), and plasma aldosterone concentrations (r=-0.87, P=0.00009) (eg, the greater the salt sensitivity and the lower the activity of the renin-angiotensin-aldosterone system, the greater improvement in insulin sensitivity). No such relationships were observed in women. In conclusion, increased salt sensitivity and decreased activity of the renin-angiotensin-aldosterone system predict improved insulin sensitivity with high-salt intake compared with low-salt intake in men, suggesting an interaction among salt intake, salt sensitivity, the renin-angiotensin-aldosterone system, and insulin action.

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.

High-performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometric method for the analysis of catecholamines and metanephrines in human urine

An assay of norepinephrine (NE), epinephrine (E), dopamine (DA), normetanephrine (NE) and metanephrine (MN) based on high-performance liquid chromatography (HPLC) in combination with atmospheric pressure chemical ionization mass spectrometry (APcI-MS) is described. The catecholamines and metanephrines were extracted from urine and aqueous samples using Bio-Rex 70 cation-exchange resin and subjected to analysis by HPLC/APcI-MS. The separation was performed on a C18 column in 50 mM ammonium formate buffer, pH 3.0, using a flow rate of 0.8 mL/min. Acetonitrile was added post-column at a flow rate of 0.2 mL/min via a post-column addition tee. The total analysis time was 6.5 min. The quantitative analysis was performed using 3,4-dihydroxybenzylamine (DHBA) as the internal standard (I.S.). Selected ion monitoring detection was applied: m/z 170 (for NE), 184 (for E and NM), 154 (for DA), 198 (for MN) and 140 (for DHBA, I.S.). The limits of quantitation were 5 ng/mL for NE, E and DA and 2.5 ng/mL for NM and MN. The recovery ranged from 75 to 83% for each analyte. The method was found to be simple and highly selective for the determination of catecholamines and metanephrines in the urine of patients suspected of pheochromocytoma.

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%).

Reduction of sympathetic hyperactivity by enalapril in patients with chronic renal failure

BACKGROUND

Inhibition of angiotensin-converting enzyme (ACE) reduces the risk of cardiovascular problems in patients with chronic renal failure. This effect may be due in part to a decrease in sympathetic nervous activity, but no direct evidence of such an action is available.

METHODS

We studied muscle sympathetic-nerve activity in 14 patients with hypertension, chronic renal failure, and increased plasma renin activity before, during, and after administration of the ACE inhibitor enalapril. Ten other patients with similar clinical characteristics were studied before and during treatment with the calcium-channel blocker amlodipine. Normal subjects matched for age and weight were included in both studies.

RESULTS

At base line, mean (+/-SD) muscle sympathetic-nerve activity was higher in the group of patients who received enalapril than in the control subjects (35+/-17 vs. 19+/-9 bursts per minute, P=0.004). The baroreflex curve, which reflects changes in muscle sympathetic-nerve activity caused by manipulations of blood pressure with sodium nitroprusside and phenylephrine, was shifted to the right in the patients, but baroreflex sensitivity was similar to that in the control subjects (-2.1+/-1.9 and -2.7+/-1.3 bursts per minute per mm Hg, respectively; P=0.36). A single dose of the sympatholytic drug clonidine caused a greater fall in blood pressure in the patients than in the control subjects. Treatment with enalapril normalized blood pressure and muscle sympathetic-nerve activity (at 23+/-10 bursts per minute) in the patients and shifted the baroreflex curve to the left, reflecting normal blood-pressure levels, without significantly changing sensitivity (-2.3+/-1.8 bursts per minute per mm Hg, P=0.96). In the patients who received amlodipine, treatment also lowered blood pressure but increased muscle sympathetic-nerve activity, from 41+/-19 to 56+/-14 bursts per minute (P=0.02).

CONCLUSIONS

Increased sympathetic activity contributes to hypertension in patients with chronic renal disease. ACE inhibition controls hypertension and decreases sympathetic hyperactivity.

Fluorogenic reactions for biomedical chromatography

A number of fluorogenic reactions, which have been used for HPLC detection systems by means of pre- and/or postcolumn derivatization, are surveyed with respect to both sensitivity and selectivity for the determination of biomedically important substances. For the derivatization of the substances, two types of fluorogenic reactions, fluorescence-generating and fluorescence-tagging, have been studied. The former are usable in most instances for both pre- and postcolumn derivatization methods, and the latter only for precolumn derivatization methods. HPLC methods utilizing the fluorogenic reactions allow analytes to be detected at picomole-subfemtomole levels. In the fluorescence-generating reactions, several fluorogenic reagents possessing two or more reactive sites in the molecule, which show molecular recognition for a variety of analytes, permit facile and reproducible detection in HPLC because there are fewer interferences from biological matrices.

Cardiac pheochromocytoma

Cardiac pheochromocytoma is a rare tumour and may be difficult to localize. We present a 32-year-old male with a cardiac pheochromocytoma that was successfully resected. An initial unenhanced CT did not reveal the tumour. MIBG-scintigraphy indicated the location, but to get full information, a dynamic contrast-enhanced CT of the chest during adequate alpha and beta blockade was essential. ECG-gated MRI gave further information about the anatomical details.

Rapid and sensitive assay of dobutamine in plasma by high-performance liquid chromatography and electrochemical detection

A sensitive and specific high-performance liquid chromatographic method with electrochemical detection was developed for measuring dobutamine in human plasma samples. Following an external standard method, 0.1 ml of EDTA-glutathione plasma was diluted on ice with 0.2 ml of a 5% trichloracetic acid solution. The mixture was centrifuged, filtered, and 30 microliters were injected. Assessment was done by electrochemical detection. The assay was linear from 1 to 400 ng/ml plasma. For determination of dobutamine we also used a liquid-liquid extraction method routinely applied for plasma catecholamines. Liquid-liquid extraction requires application of 100-1000 microliters of plasma. The standard curve was linear from 0.1 to 600 ng/ml. Absolute recovery of dobutamine was 90 +/- 3% with the liquid-liquid extraction procedure and 91 +/- 3% with the protein precipitation method. For both methods dobutamine was separated on Nova-Pak C18 columns. The mobile phase used was 0.1 molar phosphate buffer-acetonitrile (80:20, v/v) with 1-octanesulfonic acid and triethylamine as ion-pair reagents. The pH was adjusted to 2.7.

Simultaneous determination of catecholamines and dobutamine in human plasma and urine by high-performance liquid chromatography with fluorimetric detection

We report a reliable fluorimetric assay for the simultaneous determination of norepinephrine, epinephrine, dopamine and dobutamine in human plasma and urine, based on liquid-liquid extraction and derivatization with the fluorogenic agent 1,2-diphenylethylenediamine prior to chromatography. The method is sensitive (detection limit 0.3-0.8 pg injected) and reproducible (coefficients of variation 1-10%), and shows good accuracy (93-98%). The method should also be used when one only wants to measure the concentrations of the natural catecholamines, in order to avoid interference by metabolites of dobutamine and by the late-eluting dobutamine itself.

Cardiovascular, neuroendocrine, and sedative responses to four graded doses of clonidine in a placebo-controlled study

Effects of four doses of the alpha 2-receptor agonist clonidine (CLO) (0.25, 0.5, 1, and 2 micrograms/kg IV) and placebo were studied in seven healthy men who volunteered in a double-blind randomized design in order to delineate possible presynaptic and postsynaptic components in the mechanism of action of CLO. Blood pressure, heart rate, plasma noradrenaline (NOR), plasma 3-methoxy-4-hydroxyphenylglycol (MHPG), plasma growth hormone (GH), and subjective sedation were monitored for a period of 1 hr following infusion of CLO. NOR and MHPG were also analyzed in urine, collected at 1 and 4 hr after the infusions. Dose-dependent decrements were observed in systolic and diastolic blood pressure and plasma NOR levels, and dose-dependent increases in subjective sedation and plasma GH. CLO did not influence plasma MHPG levels, whereas only urinary MHPG excretion was reduced 4 hr after infusion of 2 micrograms/kg CLO. Because no obvious differences between dose-response relations of plasma NOR (believed to be a presynaptic and peripheral effect), blood pressure (believed to be mainly a central presynaptic and postsynaptic effect), and subjective sedation (believed to be a central and probably postsynaptic effect) were observed, our results do not provide simple parameters to discern the multiple mechanisms of action of CLO. However, at a dose of 0.5 micrograms/kg CLO (a dose lower than that generally used) clear effects on plasma NOR, blood pressure, and sedation, but not on plasma GH (a central postsynaptic effect) or urinary MHPG (a presynaptic effect), were observed. When using CLO as a challenge test in psychiatric disorders, a design with 0.5 micrograms/kg CLO, in addition to the traditional 2 micrograms/kg CLO, may provide more information to characterize discrete abnormalities in the noradrenergic system at the level of the brainstem, the pituitary, or the peripheral sympathetic nervous system.

Determination of catecholamines in urine by liquid chromatography and electrochemical detection after on-line sample purification on immobilized boronic acid

Norepinephrine, epinephrine and dopamine in urine were measured by an automated liquid chromatographic method. After sample purification on a column containing silica-immobilized boronic acid, which showed great affinity for catecholamines at neutral pH, the catecholamines were eluted by backflushing with an acidic mobile phase and transferred to a cation exchanger for separation. Detection was performed electrochemically and the relative standard deviation was 2% for the analysis of endogenous concentrations in human urine.

Simultaneous determination of free catecholamines and epinine and estimation of total epinine and dopamine in plasma and urine by high-performance liquid chromatography with fluorimetric detection

Epinine (N-methyldopamine) is the pharmacologically active hydrolysis product of the prodrug ibopamine, which is currently being widely studied for the treatment of congestive heart failure. This paper reports a sensitive and reliable method for the simultaneous determination of free catecholamines and epinine in plasma and urine. The compounds are isolated from plasma or urine by a specific liquid-liquid extraction, derivatized with the selective fluorogenic agent 1,2-diphenylethylenediamine, and quantitated by high-performance liquid chromatography with gradient elution and fluorimetric detection. The limits of detection for the derivatized catecholamines and epinine are 0.3-0.6 pg of injected compound. Intra- and inter-assay coefficients of variation of all four compounds are good (1-8%), as are the accuracy and linearity. A method is also reported for the determination of total dopamine and epinine in plasma and urine based on the same principle. This method, in which deconjugation is accomplished by acid hydrolysis at 95 degrees C, also shows good sensitivity and reproducibility.