The relationship of free and conjugated catecholamines in plasma and cerebrospinal fluid in cerebral and meningeal disease

A sensitive liquid chromatography-tandem mass spectrometry method for determination biomarkers of monoamine neurotransmitter disorders in cerebrospinal fluid

BACKGROUND

Cerebrospinal fluid (CSF) monoamine neurotransmitters, their precursors and metabolites are essential biomarkers in the diagnosis and follow-up of monoamine neurotransmitter disorders (MNDs). However, their extra low concentrations and potential instability challenge the detection method. Here, we present a method that enables simultaneous quantification of these biomarkers.

METHOD

With propyl chloroformate /n-propanol, 16 biomarkers in 50 μL of CSF were derivatized in situ within seconds under an ambient temperature. The derivatives were extracted by ethyl acetate and separated by a reverse phase column followed by mass spectrometric detection. The method was fully validated. Optimal conditions for standard solution preparation and storage, as well as CSF sample handling, were investigated. CSF samples from 200 controls and 16 patients were analyzed.

RESULTS

The derivatization reaction stabilized biomarkers and increased sensitivity. Most biomarkers were quantifiable in concentrations between 0.02 and 0.50 nmol/L that were sufficient to measure their endogenous concentrations. The intra- and inter-day imprecision were < 15% for most analytes, and accuracy ranged from 90.3% to 111.6%. The stability study showed that standard stock solutions were stable at -80 °C for six years when prepared in the protection solutions; Analytes in CSF samples were stable for 24 h on wet ice and at least two years at -80 °C; But repeated freeze-thaw should be avoided. With this method, age-dependent reference intervals for each biomarker in the pediatric population were established. Patients with MNDs were successfully identified.

CONCLUSION

The developed method is valuable for MNDs diagnosis and research, benefiting from its advantages of sensitivity, comprehensiveness, and high throughput.

The UDP-glucuronosyltransferases of the blood-brain barrier: their role in drug metabolism and detoxication

UDP-glucuronosyltransferases (UGTs) form a multigenic family of membrane-bound enzymes expressed in various tissues, including brain. They catalyze the formation of β-D-glucuronides from structurally unrelated substances (drugs, other xenobiotics, as well as endogenous compounds) by the linkage of glucuronic acid from the high energy donor, UDP-α-D-glucuronic acid. In brain, UGTs actively participate to the overall protection of the tissue against the intrusion of potentially harmful lipophilic substances that are metabolized as hydrophilic glucuronides. These metabolites are generally inactive, except for important pharmacologically glucuronides such as morphine-6-glucuronide. UGTs are mainly expressed in endothelial cells and astrocytes of the blood brain barrier (BBB). They are also associated to brain interfaces devoid of BBB, such as circumventricular organ, pineal gland, pituitary gland and neuro-olfactory tissues. Beside their key-role as a detoxication barrier, UGTs play a role in the steady-state of endogenous compounds, like steroids or dopamine (DA) that participate to the function of the brain. UGT isoforms of family 1A, 2A, 2B and 3A are expressed in brain tissues to various levels and are known to present distinct but overlapping substrate specificity. The importance of these enzyme species with regard to the formation of toxic, pharmacologically or physiologically relevant glucuronides in the brain will be discussed.

Determination of Serotonin and Dopamine Metabolites in Human Brain Microdialysis and Cerebrospinal Fluid Samples by UPLC-MS/MS: Discovery of Intact Glucuronide and Sulfate Conjugates

An UPLC-MS/MS method was developed for the determination of serotonin (5-HT), dopamine (DA), their phase I metabolites 5-HIAA, DOPAC and HVA, and their sulfate and glucuronide conjugates in human brain microdialysis samples obtained from two patients with acute brain injuries, ventricular cerebrospinal fluid (CSF) samples obtained from four patients with obstructive hydrocephalus, and a lumbar CSF sample pooled mainly from patients undergoing spinal anesthesia in preparation for orthopedic surgery. The method was validated by determining the limits of detection and quantification, linearity, repeatability and specificity. The direct method enabled the analysis of the intact phase II metabolites of 5-HT and DA, without hydrolysis of the conjugates. The method also enabled the analysis of the regioisomers of the conjugates, and several intact glucuronide and sulfate conjugates were identified and quantified for the first time in the human brain microdialysis and CSF samples. We were able to show the presence of 5-HIAA sulfate, and that dopamine-3-O-sulfate predominates over dopamine-4-O-sulfate in the human brain. The quantitative results suggest that sulfonation is a more important phase II metabolism pathway than glucuronidation in the human brain.

Perioperative concentrations of catecholamines in the cerebrospinal fluid and plasma during spinal anesthesia

BACKGROUND

Catecholamine release is a physiological response to stress. The extent to which perioperative stress provokes the central release of catecholamines, which modulate pain perception in the spinal cord, still remains unknown. The perioperative course of catecholamine concentrations in the cerebrospinal fluid (CSF) and plasma was examined.

METHODS

A prospective study was performed in 25 patients (ASA III, 60-84 years) undergoing elective hip joint replacement in spinal catheter anesthesia. The concentrations of dopamine, epinephrine and norepinephrine in the CSF and plasma were measured before anesthesia, immediately after surgery, and 6 and 24 h post-operatively.

RESULTS

In most patients, dopamine and epinephrine were not detectable in CSF. CSF-norepinephrine concentrations decreased from median [interquartile-range] 159 [124;216] pre-anesthesia to 116 [79;152] pmol/l immediately post-operatively and were slightly elevated 24 h post-operatively (180 [134;302] pmol/l) (P=0.05). Dopamine plasma concentrations were not detectable or were barely above the detection threshold. Plasma epinephrine increased from 61 [28;77] pmol/l pre-anesthesia to 112 [69;138] pmol/l 6 h post-operatively and returned to baseline 24 h post-operatively (P=0.001). Plasma norepinephrine concentrations increased intra-operatively from 298 [249;422] to 556 [423;649] pmol/l and remained elevated 24 h after surgery (P=0.009). There was no association between changes in CSF or plasma norepinephrine or epinephrine concentrations and changes in heart rate (HR) or mean arterial pressure (MAP).

CONCLUSION

During spinal anesthesia for elective hip joint replacement, norepinephrine concentrations were greater in plasma than in CSF. CSF dopamine and epinephrine concentrations were essentially undetectable. The changes in CSF-norepinephrine concentrations and the changes of plasma norepinephrine concentrations showed no association with each other; nor were there correlations between clinical stress parameters (HR, MAP) or visual analog scale pain, and the changes in CSF norepinephrine concentrations.

Potential role of cerebral cytochrome P450 in clinical pharmacokinetics: modulation by endogenous compounds

Cytochrome P450 (CYP) enzymes catalyse phase I metabolic reactions of psychotropic drugs. The main isoenzymes responsible for this biotransformation are CYP1A2, CYP2D6, CYP3A and those of the subfamily CYP2C. Although these enzymes are present in the human brain, their specific role in this tissue remains unclear. However, because CYP enzymatic activities have been reported in the human brain and because brain microsomes have been shown to metabolise the same probe substrates used to assess specific hepatic CYP activities and substrates of known hepatic CYPs, local drug metabolism is believed to be likely. There are also indications that CYP2D6 is involved in the metabolism of endogenous substrates in the brain. This, along with the fact that several neurotransmitters modulate CYP enzyme activities in human liver microsomes, indicates that CYP enzymes present in brain could be under various regulatory mechanisms and that those mechanisms could influence drug pharmacokinetics and, hence, drug response. In this paper we review the presence of CYP1A2, CYP2C9, CYP2D6 and CYP3A in brain, as well as the possible existence of local brain metabolism, and discuss the putative implications of endogenous modulation of these isoenzymes by neurotransmitters.

Inhibition of cytochrome P450 2C9 activity in vitro by 5-hydroxytryptamine and adrenaline

In the present study, the occurrence of a modulatory effect of 14 neurotransmitters, precursors and metabolites on the cytochrome P450 2C9 (CYP2C9) enzyme activity, as determined by diclofenac 4-hydroxylation, was studied in human liver microsomes. Two indoleamines, 5-hydroxytryptamine (5-HT) and adrenaline, showed a non-competitive-type inhibitory effect of approximately 90% of the diclofenac 4-hydroxylase activity, with Ki values of 63.5 (0.7 and 156 (89.3 microM, respectively. The rest of substances analysed were weak inhibitors or had no inhibitory effect. CYP2C subfamily is present in human brain, although CYP2C9 isozyme has not yet been identified in this tissue, and CYP2C9 is involved in the metabolism of psychoactive drugs. Therefore, the fact that endogenous compounds could modulate the CYP2C9 activity, suggests that an hypothetical local activity of brain CYP2C9 might be susceptible to regulatory mechanisms. The possible clinical implications of this modulation are discussed.

Total free catecholamines assay by identification of its two functional groups and micro-flow injection chemiluminescence

We have developed a novel method of assaying total free catecholamines using sulphuric acid-derivatized beads for extracting and identifying catecholamine (CA) on the surface, and assaying the peroxide produced from CA by chemiluminescence (CL). Current assay methods for CA by electrochemical determination, fluorescence and chemiluminescence need a time-consuming separation by high-performance liquid chromatography. We eliminated this separation step by identifying the two functional groups of CA using a derivatized bead and this resulted in a highly specific CA assay. The principle is as follows: the amino group of CA was trapped by ion binding with a sulphuric acid derivative immobilized on a bead, and the diol of the CA bound to the bead was converted to peroxide with imidazole under alkaline conditions. The peroxide produced was assayed by microflow injection-horseradish peroxidase-catalysed luminol chemiluminescence. We synthesized three types of sulphuric acid-derivative immobilized beads (6.5 mm i.d.). The types of immobilized sulphuric acid derivative used were straight-chain, branched chain and benzenesulphonic, respectively. The order of the three types of beads for extracting CA was: bezenesulphonic type > branched type > straight-chain type. The optimal incubation time for generating peroxide was 30 min. The peroxide generated in the reaction solution was stable with within-run reproducibility of CV 5. 7% after incubation for 80 min. The regression equation of a standard curve for dopamine was Y = 12.8 X(2) + 476X - 373 (where Y = light intensity (RLU), X = concentration of dopamine (micromol/L)). The minimum detection limit of dopamine was 0.1 micromol/L, and the within-run reproducibility of dopamine (10.5 micromol/L) was CV 4.7% (n = 5). This method is applicable to assay of total free CA without use of HPLC.

The effects of dopamine and serotonin on rat dorsal root ganglion neurons: an intracellular study

The effects of bath application of dopamine and serotonin (10(-10)-10(-8) M) were studied in the superfused dorsal root ganglia of 30-36-day-old rats by means of the intracellular technique. In the majority of cells, dopamine and serotonin caused depolarization (60% and 64% of the tested cells, respectively). In other cells hyperpolarization, biphasic reactions or absence of responses have been observed. All reactions were dose dependent and reversible. Depolarization was accompanied by a decrease of input membrane resistance and hyperpolarization by its increase. Some cells did not show these alterations. Monoamines were also capable of modulating spikes. In some cases dopamine (10(-8)-10(-7) M) decreased the amplitude of the action potential and increased its duration, but the same concentration of serotonin produced the opposite effect on these parameters. The correlation between the electrophysiological properties of the dorsal root ganglion neurons and their responses to monoamines were discovered. Neurons with high input membrane resistance, prolonged action potential and slow conduction velocity (small cells) were influenced much more by monoamines than neurons with low input membrane resistance, "fast" action potential and rapid conduction velocity (large cells). (1) Small cells had lower threshold to monoamines (10(-8)-10(7) M) than large ones, some of which did not respond even to 10(-6) M. (2) The amplitude and duration of monoamine-induced depolarization in small cells were on average about two to three times higher than those in large cells. These data provide evidence for the modulatory role of monoamines in spinal afferent sensory functions.

Biogenic amines and their metabolites in body fluids of normal, psychiatric and neurological subjects

The biogenic monoamines and their metabolites have been isolated, identified and quantified in human body fluids over the past forty years using a wide variety of chromatographic separation and detection techniques. This review summarizes the results of those studies on normal, psychiatric and neurological subjects. Tables of normal values and the methods used to obtain them should prove to be useful as a reference source for benchmark amine and metabolite concentrations and for successful analytical procedures for their chromatographic separation, detection and quantification. Summaries of the often contradictory results of the application of these methods to psychiatric and neurological problems are presented and may assist in the assessment of the validity of the results of experiments in this field. Finally, the individual, environmental and the methodological factors affecting the concentrations of the amines and their metabolites are discussed.

Epinephrine in mammalian brain

1. Epinephrine is widely distributed in brains of various species throughout phylogeny but maintains its localization to hypothalamus and brainstem/medulla in all species studied. 2. A general decrease in brain epinephrine content is observed phylogenetically beyond fishes with wide variation within species. 3. The cellular localization of epinephrine forming enzyme is dissociated from epinephrine stores in hypothalamus where epinephrine appears to be primarily a hormone. 4. Three proposed functional pools of epinephrine are described. Synthesis of a hormonal pool and a second, perhaps nonfunctional, pool co-stored in noradrenergic terminals in the forebrain occurs extraneuronally and is probably inhibited acutely in the presence of high corticosteroids due to inhibition of uptake 2. Synthesis of epinephrine in the neuronal pool found primarily in the medulla may be enhanced due to increased PNMT activity in the presence of elevated corticosteroids. 5. Phylogenetic and pharmacological data suggest that epinephrine may play an important role in tonic regulation of the level of arousal, reward and sensitivity to environmental stimuli in mammals.

Effect of ganglion blockade on cerebrospinal fluid norepinephrine

The source of norepinephrine (NE) in CSF has been unclear. It has been suggested that CSF NE indicates central neural noradrenergic tone and is determined differently from plasma NE. If CSF NE depended specifically on NE release in the CNS, then interference with ganglionic neurotransmission would be expected to decrease plasma NE but not CSF NE. Hypotension caused by ganglionic blockade might be expected to increase CSF NE reflexively. We infused the ganglion blocker, trimethaphan, intravenously into anesthetized dogs and measured the effects on mean arterial blood pressure (MAP) and on cisterna magna CSF levels of NE. The results were compared with those obtained on administration of saline, clonidine (2 micrograms/kg), yohimbine (0.25 mg/kg), or nitroprusside and with those obtained when hypotension during ganglion blockade was prevented by concurrent treatment with phenylephrine. Trimethaphan decreased MAP by 40%, arterial NE by 64%, and CSF NE by 61%. Nitroprusside administered intravenously to produce the same 40% depressor response increased arterial NE by 612% and CSF NE by 155%. Prevention of ganglion blockade-induced hypotension using phenylephrine did not prevent the decrease in CSF NE caused by trimethaphan, and when phenylephrine was discontinued, the resulting hypotension was not associated with increases in CSF NE. The similar decreases in plasma NE and CSF NE during ganglionic blockade, and the abolition of reflexive increases in CSF NE during hypotension in ganglion-blocked subjects, cast doubt on the hypothesis that CSF NE indicates central noradrenergic tone and are consistent instead with at least partial derivation of CSF NE from postganglionic sympathetic nerve endings.

Hemophilus influenzae meningitis in the rat: behavioral, electrophysiological, and biochemical consequences

Hemophilus influenzae is the most common cause of bacterial meningitis in children, and a high percentage of survivors are at risk for long-term sequelae. To explore the mechanisms responsible for these sequelae, a neonatal rat model was used to define the behavioral, electrophysiological, and biochemical changes following meningitis. Three days after inoculation of 6-day-old rats with a minimum of 1 X 10(7) colony-forming units of a virulent Hemophilus influenzae, type b, cerebrospinal fluid and blood were cultured to confirm the presence of meningitis and bacteremia, respectively. At this time, forebrain norepinephrine and dopamine levels were significantly elevated in meningitic rats when standardized on a wet-weight basis. No changes in brain serotonin or heart norepinephrine levels could be found in the 9-day-old rats. No residual changes were found in steady-state concentrations of norepinephrine or dopamine in surviving adult rats. However, survivors that had had meningitis as neonates showed significant impairment in active and passive avoidance learning tasks and demonstrated a significantly higher level of activity during a habituation period in circular photocell activity cages. No change in the flinch-jump threshold was detected. Brainstem auditory evoked potentials showed delays of various waves in 3 of 10 Hemophilus influenzae type b-treated adult rats tested. These rats also exhibited markedly augmented locomotory responses to d-amphetamine (1 mg/kg), suggesting a long-lasting perturbation of central monoamine neuronal transmission.

CSF dopamine levels correlate with extraversion in depressed patients

Cerebrospinal fluid (CSF) dopamine levels were studied in 16 male patients who also were tested for self-reported extraversion using the Eysenck Personality Inventory. Log CSF dopamine was significantly correlated with extraversion as predicted by recent theoretical work integrating mesolimbic dopamine function and active responding to external incentives as psychobiological traits. CSF dopamine levels were uncorrelated with the total score on the Hamilton Rating Scale for Depression, self-reported neuroticism, and age. The results are discussed in relation to other biological models of extraversion such as the construct of sensation-seeking behavior.